The relationship between Elena, Jeremy and Jenna, they used to live together after the death of Elena's adoptive parents and Jeremy's parents and also Jenna's sister and brother-in-law Miranda Sommers-Gilbert and Grayson Gilbert. Jenna was their legal guardian. Their bond have grown closer together throughout the series, but this bond was destroyed, as Jenna was killed by Klaus in The Sun Also Rises. In the first season, Jenna goes to school for a meeting and the matter is Jeremy, who was missing classes, and using drugs. So she is humiliated by the teacher, who is killed a few episodes after.
Besides being Elena's aunt she is her best friend, the two used to exchange secrets, until this link was broken when Stefan told Elena that she was adopted, and she stayed away form Jenna. Jeremy and Jenna had a normal relationship.
In the first season the relationship between Jenna and Jeremy, who unlike Jenna and Elena's relationship is very difficult. The relationship between Jenna and Elena is strong. Jenna is trying to stop Jeremy from using drugs, which makes it more difficult for Jeremy who was addicted. Elena discovers she is adopted and a certain distance between her and Jenna appears, Jenna tries to help Elena find her biological parents as a way of apology. Jenna soon discovers that Elena's mother is her boyfriends "missing" wife. Both Elena and Jeremy know about supernatural being but still Jenna doesn't.
During the second season, Jenna discovers that everyone including, Elena, John, Isobel and Alaric knew about Elena's biological parents, damaging the relationship she had with Elena and Jeremy. When Jenna discovers that Elena and Alaric have concealed the fact that Isobel is still alive and she is the real mother of Elena and was the wife of Alaric, Jenna falls into deep despair and distrust. Jenna eventually finds out that vampires and witches exist.
Elena ends up telling her about all the secrets that everyone has been keeping from her. Shortly after the return of Alaric, Jenna forgives him, and they resume there relationship. She then soon feels more connected with her family and friends, but Klaus abducts her, and she became a vampire. Damon tells Jeremy and Alaric that Jenna will be used in sacrifice, Jeremy is very concerned and tries to go help rescue Elena and Jenna, but Bonnie stops him. Unfortunately, Elena witnesses Jenna's death and is powerless to stop it. After the sacrifice, Damon is the one to tell Alaric and Jeremy about Jenna's death, which leaves them both devastated.
Jeremy and Elena try to get ahead but Elena feels guilty of all deaths in the Gilbert family, but Jeremy says that they are still together. Showing they are now attempting to move on. Alaric does not share the same positive outlook as Elena and Jeremy, as he is shown drinking, and having a very depressed and bleak look on the situation of Jenna's death. But Damon's near death causes him to come out of his shell, and return to the world. He is shown to be improving by the end of the season two finale.