''Rose'' (season 2, episode 8)
What happened: After the Salvatore brothers teamed to rescue Elena from Elijah (in his first appearance in the series), Elena ran to Stefan not Damon.
Why it's essential: The brothers recognized they wouldn't be able to keep Elena safe from Klaus if they let her come between them like her doppelgänger (and their sire) Katherine had.
Essential exchange: Damon, telling Elena that he loved her was the most selfish thing he'd ever done: ''And it's because I love you that I can't be selfish with you, why you can't know this. I don't deserve you. But my brother does.'' (Then he compelled her to forget everything he'd just said. But as a vampire, she now remembers.)

''As I Lay Dying,'' (season 2 finale, pictured)
What happened: Damon received a lethal werewolf bite from Tyler.
Why it's essential: On his deathbed, with Elena by his side, Damon essentially admitted defeat. He told her he knew she loved Stefan, and that it would always be Stefan, but he wanted her to know he loved her, too. She admitted she also had feelings for him and kissed him gently.
Essential exchange:
Damon: You should have met me in 1864. You would have liked me.
Elena: I like you now. Just the way you are.
How it played out: After Katherine arrived with the cure — Klaus' blood, which Stefan had procured by agreeing to become Klaus' wingman and sacrifice all that Elena liked about him — the fight for Elena's heart became a fair one.

''Heart of Darkness'' (season 3, episode 19)
What happened: After learning of the sunlit dream Damon gave Rose on the day she died, Elena saw another side of him — mainly how hot he looked in a motel room with his shirt hanging open. And this happened.
Why it's essential: Damon reminded Elena she would have to accept the good and bad in him. Judging from their makeout session, her resistance to his darker side was majorly fading.
How it's still in play: In season 4's ''My Brother's Keeper,'' Elena and Damon finally had sex. But is her heightened lust for him now that she's a vampire a sign of true love, or the result of her sire bond? In season 4's ''O Come, All Ye Faithful,'' Damon set Elena free and told her to keep her distance.