Dating Timeline: TV Series

First Relationship:

Start Up: The Night of the Comet (1x02)

Break Up: Lost Girls (1x06)

Reason: Elena finds out that Stefan is a vampire.

Second Relationship:

Start Up: The Turning Point (1x10)

Break Up: Plan B (2x06)

Reason: Katherine wanted Elena and Stefan to break up and to prove it she attacks Jenna. So for the sake of anyone she loves getting be killed, Elena does what Katherine wants, and tearfully breaks up with Stefan, despite how much she doesn't want to.

Third Relationship:

Start Up: Rose (2x08)

Break Up: The End of the Affair (3x03)

Reason: Elena and Damon go in Chicago to save Stefan. But by the time she was there to save Stefan, Stefan rejects Elena and said that he doesn't want be saved; he lies and says he doesn't want her anymore.

Fourth Relationship:

Start Up: Growing Pains (4x01)

Break Up: We All Go A Little Mad Sometimes (4x06)

Reason: Elena admitted to Stefan that since she became a vampire, her feelings for Damon intensified . Her desires became darker and she wasn't the same girl that chose him on the Wickery Bridge. Stefan couldn't deal with it anymore and consequently broke up with Elena.