Elena and Bonnie were originally best friends, whilst Caroline was closer to Bonnie, mainly due to being jealous of Elena. After Caroline's transformation into a vampire, her friendship with Bonnie deteriorated for a short time, but Elena was there for her, strengthening their friendship. Bonnie later accepted Caroline the way she was, and they quickly rekindled their close friendship. Unfortunately, on the night before graduation, Bonnie desperately attempted to bring Elena's brother Jeremy back to life using spirit magic, dark magic, and Expression magic all at the same time, and ultimately died from overuse of magic. Not wanting to hurt Caroline and Elena, Bonnie, as a ghost, forced Jeremy to keep her death a secret for the entire summer. Because the veil was down when Bonnie died, Bonnie was able to graduate with her friends with no one else the wiser. Once Caroline and Elena learned of Bonnie's death, they worked tirelessly to find a way to bring her back, eventually convincing a witch to give Bonnie the power to be the Anchor to the Other Side, allowing her to be a corporeal ghost so she could continue to live as a normal human would, though she also acted as a tollbooth to the Other Side, which brought complications.
After Markos tore his way out of The Other Side, it began falling apart, which not only threatened the residents of the supernatural purgatory with permanent extinction, but also Bonnie, as the Anchor. Once again, Bonnie attempted to keep Elena and Caroline from knowing about her imminent demise, though they eventually did find out and tried their best to stop her. In the end, they failed, as the Other Side completely collapsed and destroyed itself, taking Bonnie and Damon into an unknown dimension with it.
Caroline approached Elena and Bonnie at school, offering her sympathies to Elena for her parents' deaths. Caroline later confessed to Bonnie that she was jealous of Elena. When Caroline arrived at cheerleading practice with Damon, Elena explained to Bonnie who he was. When Bonnie complained about going to the party alone, Caroline told her to go with Elena.
When Caroline and Bonnie fell out over the crystal, Elena tried to fix their friendship. Bonnie told Caroline she was a witch, something Elena already knew, and Caroline eventually apologised, confessing that Bonnie would always be her best friend. Caroline then suggested they have a séance, and they ended up channeling Emily's spirit which possessed Bonnie. Caroline didn't believe her and went home, whilst Elena did and called Stefan for help. At a school dance, Bonnie and Caroline attended together and mocked Elena over having a "threesome" with Stefan and Damon.
On a double date with Stefan and Matt, Caroline confessed to Elena that she was always second choice as Matt was still in love with Elena and Bonnie considered Elena her best friend.
After Bonnie's grandmother died, she distanced herself from Elena, becoming closer to Caroline, however she still defended her when Caroline was insensitive toward Elena. Caroline became determined to fix Elena and Bonnie's friendship, determined to find out what was wrong. When Isobel visited Elena, she pointed out Bonnie, Caroline, and Matt as possible targets.
In Brave New World, Bonnie, Elena, and Damon discuss Caroline in hospital. Damon offers to give her some blood and Bonnie tells him to do it for Elena, reminding them that its Caroline and they can't let her die. Bonnie and Elena cover for Caroline at the carnival. After discovering Caroline has been turned into a vampire, Bonnie tries to kill Damon, blaming him, and terminates her friendship with Caroline. Meanwhile, Elena stops Damon from killing Caroline.
In Plan B, Stefan is trapped in the well full of vervain and Elena calls to Carolin for help. Bonnie and Caroline walked at human speed to the old Lockwood well in the woods Caroline hears Elena's cries for help. She rushed to her aid at super speed until she reached the well, Elena told Caroline that Stefan was trapped in the well (it was Bonnie who texted him with the location of the moonstone). Caroline made a move to dive down but Elena told her that it was filled with vervain.
Caroline looked for something and found a chain in a neat pile. She took the end of the chain and threw it over the cross bar. A few moments later Elena had tied the end of the chain around her waste like a harness and was getting ready for Caroline to lower her down inside. At that moment Bonnie finally caught up asking what happened saying Caroline just took off in a blur. Caroline explained that she heard Elena screaming and urged Bonnie to help Elena over the lip of the well. They manage to get to Stefan and they rescued him. As Bonnie continues to rebuff Caroline, Elena and Caroline grow closer.
In Daddy Issues, After Caroline was tortured by the werewolves, Stefan asked for Elena and Bonnie's help and they arrived at Caroline's for a sleepover. They all share Caroline's bed and Caroline kicks Elena out when her phone starts to ring, telling her to answer it.
In Crying Wolf, When Elena and Stefan leave town, Caroline and Jeremy help Bonnie get information out of Luka involving Elena.
In The House Guest, Bonnie, Caroline and Elena decide to have a girls night. Jenna walks in depressed and they soon convince her to stay and join them. Trying to decide what to do, Caroline tells them about the band playing down at the Mystic Grill and they all decide to head on out. Caroline, Elena, and Bonnie go to the Grill with Jenna where they support Caroline as she serenades Matt with Eternal Flame. Then Elena, Bonnie, and Caroline get news of Klaus coming after Elena.
In The Sun Also Rises, Caroline, Elena and Bonnie is also seen with Jeremy, Stefan, Damon and Alaric at John and Jenna's funeral.
In Disturbing Behavior, Caroline and Bonnie arrive unexpectedly at Elena's. They catch up in the kitchen as Bonnie was away for the summer. Bonnie says her father's side of the family is boring, but Caroline says she would love a normal family after all she's been through. Elena's necklace then burns her and Bonnie, the spell giving off an electric current. At the latest Mystic Falls celebration, Caroline, Bonnie, and Elena are on the outskirts of the event as they try to figure out what's wrong with Elena's necklace.
While Bonnie reads up on an identification spell that she thinks will be useful, Caroline sees seizes the opportunity to question Elena about her motives with Damon and if she's switching Salvatores. Elena says her and Damon are searching for Stefan, nothing more. Caroline explains that if her father can't change her, there's no hope for Damon to change. Bonnie then tells them to look at the necklace, that is now floating in the air. That evening, Caroline and Elena continue to speculate about the necklace despite that they're amongst a group of supernatural-hating Founding Family members.
In The Reckoning, Caroline, Elena, Bonnie, and Tyler prepare for Senior Prank Night and Caroline gets mad at Matt, who forgot. Caroline, Elena, and Bonnie later start senior year. Caroline becomes determined that they will move on and have a good year together.
In Smells Like Teen Spirit, Caroline, Elena, and Bonnie stand amongst a group of overly excited students outside school. It's their first day of senior year, but they don't look like they're looking forward to it. Caroline decides to accept everything that's happened and encourages Bonnie and Elena.
In Our Town, is Caroline's birthday and she's surprised with an enthusiastic Elena, Bonnie, and Matt wishing her a happy birthday. Elena explains that because Caroline ditched school she missed out on their "birthday work of art" displayed on her locker, so they're bringing the party to her. Caroline doesn't try to hide how disinterested she is.
Caroline points out she's frozen and is never going to be eighteen. Bonnie, Elena, Caroline, and Matt walk into a strange old building that's in the middle of the woods. Elena says that instead of a birthday, Caroline needs a funeral in order to mourn her old life and move on. Elena, Matt, and Bonnie list Caroline's human qualities and accomplishments. Bonnie uses her powers to light the candles on Caroline's cake and Elena asks Caroline to make a wish. Later, Elena, Bonnie, Matt, and Caroline are still held up in the creepy building. Caroline is busy on her phone and Elena is skeptical about what she's doing.
Caroline admits that she might have text messaged Tyler. Bonnie defends Caroline and turns on Elena, mad at her for having Damon compel Jeremy to leave town. Matt intervenes and Bonnie leaves.
In The Murder of One, Elena goes to the Salvatore boarding house and sees Damon and Rebekah together, she gets upset knowing that they slept together. Angry, she leaves and goes to Caroline's house, where they try a privacy spell with Bonnie. After their plan for kill to a original fails and Bonnie's mother is turned into a vampire, Elena hears the news and the price of saving her, leading her to seek Bonnie who is watching over Abby who is in transition. Caroline asks her to leave, because even though Bonnie is alright since the goal was to save her friend it seems that Bonnie is the one who always gets hurt. Elena decides to leave but asks Caroline to tell Bonnie about her gratitude and love.
In We'll Always Have Bourbon Street, Elena invites Caroline and Bonnie to the Salvatore Boarding House to have a girls' night. they are dancing, drinking and Bonnie is taking some photos in the living room. In the next scene they are in Damon's bath and a discussion between Elena and Caroline about Damon begins, while Bonnie share just some toughts about the things Elena and Caroline are arguing.
Caroline decides to tell Elena that she is sired with Damon and they start arguing about it, then Elena ask Caroline to leave while Bonnie stare at the scene, then two hybrids arrive and Elena and Caroline start fighting with them, then while Bonnie is making a spell to protect Caroline and Elena one of the hybrids tell Bonnie that a hybrid bite is enough to kill Caroline, so Bonnie stop the spell and the hybrids leave with Caroline.
In Stand By Me, Caroline is glad to see Bonnie, As Bonnie told Matt, Caroline, and Elena what she needed to do, we flashed back to Shane telling Bonnie on the island: So Qetsiyah knew Silas would want to die and be with his true love, so she created "the Other Side" -- a purgatory for all supernatural beings -- insuring that if he did die, he’d end up there forever. So Silas needs Bonnie to get rid of the Other Side. If she drops the veil, then ALL the supernatural creatures who’ve ever died since the Other Side was created will be back, including Grams and Jeremy. Shane told Bonnie she would do this. Caroline, of course, immediately said this was crazy talk, and Matt agreed. Bonnie fought with them and Elena just stared ahead.
In Pictures of You, Caroline gets ready for Prom with Bonnie helping her dress shopping. When Elena arrives at the store, Caroline and Bonnie leave then Elena steals the dress.
In I Know What You Did Last Summer, Caroline and Elena are excited to go to college but Bonnie only can accompany them as a ghost. They reach their dormroom and begin unpacking, they meet their new roommate Megan, this unexpected roommate bothers Caroline, since they were expecting Bonnie to be their roommate.
In For Whom the Bell Tolls Jeremy finally reveals the truth about Bonnie's death. Elena is shown to be extremely upset while trying to find a funeral dress, and breaks down in Damon's arms. At Bonnie's memorial, both Elena and Caroline comfort one another while Jeremy relays Bonnie's message to the group.
In Monster's Ball Elena is shown to be feeling guilty over not figuring out Bonnie's death sooner than she did.
In Handle with Care, Elena and Damon work together with Silas to help find and destroy the anchor to the other side, and in return Silas will use his powers to bring Bonnie back to life.
In Death and the Maiden, after Silas fails to keep his promise Elena works together with Qetsiyah in order to transfer the anchor from Amara to Bonnie. Caroline and Elena are present in the moment that Bonnie is resurrected, they are very happy and Caroline immediately reminds Bonnie will be their roommate in college.
In Dead Man on Campus, Caroline and Elena are organizing a party at the University for the return of Bonnie and for all the good events recent as Silas dead.
In 500 Years of Solitude, Caroline is very excited about the break up between Damon and Elena. She and Bonnie prepared a breakfast break for Elena but then receive a call from Stefan who informs them that Katherine is dying.
Later , Caroline, Elena and Bonnie arrive to the Salvatores's house and Damon, Jeremy and Matt are celebrating the imminent death of Katherine, they joined to the others and start to drink too. Later Nadia appears, she is looking for help to carry out a plan to save Katherine's life but nobody want to help, so she threat them telling that she has kidnapped to Matt locked in the safe where Stefan was.
In Total Eclipse of the Heart, Caroline, Bonnie and Katherine who is still posing as Elena, attend college classes, they walks into a classroom and Caroline is talking about a fresh start in her life as single. Caroline decides to move on from her relationships with Tyler and Klaus and asks Bonnie and Elena to attend at Bitter Ball with her. she tells Bonnie to assist without the company of Jeremy what Bonnie accepts, the three agree to attend the dance.
In Home, Everyone is going through Bonnie to return to life, Elena back from the other side but she isn't happy because Bonnie forces her to return and Damon is still in the other side, Caroline start asking for Stefan because he still hasn't returned, Caroline's questioning ends when Bonnie starts coughing up blood, she is worried about her friend but Bonnie unintentionally touched Stefan and he returns from the other side.
Bonnie: Well, I was talking to Grams, and she said the comet is a sign of impending doom. The last time it passed over Mystic Falls, there was lots of death. So much blood and carnage, it created a bed of paranormal activity.
Caroline: Yeah, and then you poured Grams another shot and she told you about the aliens. So then what?
Caroline: The sexy suds car wash is tomorrow. The football team and the band have committed. Well, not all the band. Just the ones who could pull off the bikini. I want, in your face, sexy. I mean, it's a fund raiser, for god's sake.
(At Elena's house. Caroline walks into the living room to apologize to Bonnie.)
Caroline: Bonnie. Look, it's just not me. I don't believe in the...But if you do,then...Okay. I'm in.That's all it takes for me to jump on board,because I consider you to be my best friend. And I'm saying this knowing that Elena's in the kitchen listening to my every word. Look, I didn't know how real this was for you,but I'm listening now. Okay? Elena, you can come in now. We're done. (Elena enters.)There is just way too much drama in this room.So what do you guys wanna do?I have an idea.Why don't we have a séance?
(Elena grabs the box and a snake inches towards her. It wraps onto her. Elena screams and throws the snake off of her. Another snake has crawled up her arm. She backs up against the wall and pulls the box out its hiding spot. She ties the chain around herself again.)
Caroline: Hey, everybody. Let's hear it for the band! Weren't they awesome? So there's this guy. And, uh, he told me to tell him how I feel about him. Like it's so easy. Um, you know, just 'cause I talk a lot doesn't mean I always know what I'm actually talking about. Ah, like now, I'm feeling loopy and I don't really know how to express myself. I can sing. Yeah! Yeah. You know what, I'm going to sing.
Caroline: Thanks, guys. Really, I'm just not feeling my birthday this year.
Bonnie: I'm sorry, what? You've already claimed your birthday as everyone's favorite day of the year.
Caroline: Yeah, and now, it's just a reminder that technically, I'm dead. [beat] Look, I didn't even like 17. And the only point to being 17 is to get to 18. It's a filler year; I'm stuck in a filler year.
Elena: I just keep thinking…. Before the sun and the moon ritual, Elijah found a way to keep me alive. And now I’m in exactly the same position and I’m just gonna let him die? It just doesn’t feel right.
(Caroline re-enters the room.)
Caroline: Okay. First of all, this privacy spell is totally not working. Second. Elena, you are not doing this, Esther is doing this.
Bonnie: There’s no time to change your mind, Elena. He’ll be dead by the end of the night.
Caroline: So, Abby thinks Bonnie can reverse the damage of the spell. I guess this same thing happens to witches who get obsessed with dark magic. They lose control and start acting out their darkest impulses.
Elena: Don't listen to her. So, girls' night? We can raid the Salvatore wine cellar.
Caroline: Um, are you sure that Stefan and Damon are cool with us crashing at their place?
Elena: (She catches sight of Damon walking in the school, him motioning for her to talk to him.) I can't go home because my brother is trying to kill me. So their place is mine now, too. I'll see you in a bit.
(Elena walks away to meet Damon with Caroline and Bonnie looking on.)
(Elena has brought a wooden crate into the parlor filled with wine bottles.)
(She hands Elena her phone and Elena plays the video.)
Elena: (laughing) I look like Superman. Watch this. (She pauses the video at the point where she is superspeeding back into the room. The capture shows a giant blur behind her due to the speed at which she is running. She shows it to Bonnie and Caroline.) This year's Christmas card. (They all laugh.) Being a vampire is so weird. Oh my God, I love this bathtub. Why don't we come and hang out here more often?
Caroline: I'll tell you why. Cooties. Think of all the germ-ridden skanks that Damon has lured into his den of enequity.
Caroline: Ok, I'm sorry. I've been good all night. I am stopping now.
Elena: (sarcastically) No, don't stop on my account. Rip away. I mean, it's only Damon, right?
Caroline: Well, say what you want about Ripper Stefan, but at least he wasn't a man slut.
Caroline: I... Look, I'm sorry that it came out like that, but it's true. Damon's blood turned you. You couldn't feed from animals or blood bags because he told you so. Then he suggested that you try again with blood bags and suddenly...
(Elena turns and looks at her. Kim rushes into the house and knocks Elena into the wall. She then rushes at Caroline and grabs her by the throat. Adrian rushes in and grabs Elena who fights back and pushes him against another wall. Adrian gets the upperhand eventually and slams Elena into the wall. Both of them have their hands wrapped around the others' throat. Bonnie starts to perform a spell which is so powerful it makes the lights flicker and break.)
Bonnie: Matt and I are gonna have the sexiest date there.
Caroline: You know what? I love friend prom. And it’s exactly what prom should be, friends and memories. Yes, it’s sucks that my boyfriend can’t be here, but the three of us are going have the time of our lives.
Elena: Hey Bonnie, heard you got your mind wiped. That sucks. Pretty dress, Caroline.
Caroline: I know, you helped me pick it out months ago. When we were friends. Before you tried to kill me.
(Bonnie records a video of herself on her cellphone)
Bonnie: Hi, Mom. I know we haven't seen each other, or talked in a while... so I wanted to make you a video update. I finally finished my whirlwind summer tour, got a new 'do and, I'm in college at Whitmore, where Grams taught. And this is my dorm! It's huge, right? It even has a fireplace! I mean, what dorm has a fireplace?
(The door opens and Caroline and Elena enter.)
Bonnie: Oh, here they are. Hey, guys! Say hi to my mom! (Caroline and Elena get excited and wave to the camera.) They're planning me a welcome party. Just something, just low-key. I miss you. Please come visit when you get a chance. I'll, um, talk to you soon. Bye!
Elena (mimicking Bonnie): "By the way, Mom; I'm not a witch anymore, because I died and then came back from the Other Side."
Caroline: "Yeah, I'm this supernatural anchor that connects the two worlds together, so..."
Elena: "Technically, I'm a ghost, that people can still see, and touch, so..."
Bonnie: Okay, so I left out a detail...or two. I'll explain when she visits. How big is this party going to be?
Elena: Well, let's see. Silas and Tessa are gone, and you finally aren't.
Caroline:: Which equals a massive cause for celebration!
Elena: Which equals a massive party. Hopefully. I mean, since each of us have only made one friend in college so far.
Caroline: And given that mine went radio silent after he kissed me, and yours was last seen at a tea party for a vampire-hating secret society.
Bonnie: Hmm... Augustine, right? The one who covered up your roommate's death and wants you kicked off from campus.
(Both girls give her a look.)
Bonnie: What? I've kept up! The Other Side is boring. What else am I supposed to do?
Elena: Alright. So, Augustine wants us gone. Who cares? It doesn't matter. It's not gonna happen. We're moving on with our lives, together, as functional vampires,—(pointing towards Bonnie)—a former witch, anchor-thing. I don't know. (They laugh) And we have a party.
'(As Caroline keeps taking in the background, Bonnie notices the girl next to her playing with her pen, twirling it on the seat's desk. But then, she keeps twirling it... by hovering her hand over it without touching it. Bonnie opens her eyes and mouth in surprise.)
Bonnie died in The Last Dance when Klaus seeming forced her to use too much magic trying to kill him. However, she had really cast a spell to mimic death, allowing her to appear dead to Klaus, and magically return to life later in the same episode.
Elena died in The Sun Also Rises when Klaus drank her blood. She returned in the same episode thanks to a spell Bonnie had cast that allowed John Gilbert's life force to resurrect her, at the cost of his own life.
Elena died in The Departed when Rebekah caused Matt's truck to crash into the river, leading her to drown. She returned in the same episode as a vampire.
Bonnie died in Growing Painsfrom using dark magic to temporarily stop her own heart so she could travel to the Other Side and return Elena's soul back into her body. Unfortunately, she was stopped from completing the spell by the ghost of her Grams, and she returned to life through the spell in the same episode.
Bonnie died in The Walking Dead when she used too much magic at once to resurrect Jeremy. She was later brought back to life, in a sense, when she was made a corporeal ghost as the Anchor to the Other Side in Death and the Maiden.
Elena died again in Home, when she and Damon were blown up in an explosion as part of their plan to sacrifice dozens of Travelers to bring their friends back to life from the Other Side. She returned to life as a vampire after passing through Bonnie, just as they planned.
Bonnie died for the fourth time in Home when the Other Side finally imploded. She was surrounded by a white light as she and Damon were presumably sucked into another dimension.
They used to play near the well where Mason hid the moonstone on the Lockwood property.
Matt told Katherine (while she was possessing Elena's body using a Passenger spell) that Elena likes both Caroline and Bonnie equally.
Out of the three, Bonnie has died the most and Caroline has died the least.
Elena and Bonnie have been victims of possession by Katherine Pierce and Emily Bennett, while Caroline hasn't
Ironically both girls were possessed by an ancestor from their own bloodline.