I really liked this very subtle parallel. In 3x05, Klaus had come back into town and completely traumatized Elena by compelling Stefan to kill her. And Stefan, not being able to break the compulsion, ending up hurting Elena. Elena ended the episode in a very bad state and was rescued by Damon from the hospital. In a sense, a lot of what Elena used to believe in was destroyed in this episode. She believed her and Stefan’s love could conquer anything and because Stefan couldn’t break the compulsion, she lost faith in their love (and in Stefan). And without meaning to, Elena came to the realization that she needed Damon to be there for her, no matter what, because he was always there… and his absence made her realize how much that meant to her.
What I found really interesting was that Elena needed comfort, Damon offered her bourbon, and she took it (back in 3x05). In episode 4x21, Elena is talking about how being humanity!less showed her how much humanity really means and how “things DO matter.” And this time, Elena was (and still is) very broken, but this time she had both Damon and Stefan to comfort her. Yet, despite having both of them there, when Stefan offered her the bourbon, she didn’t take it. This can be interpreted in many ways, but I took it as Elena not needing Stefan anymore. Not in the way she did back in Season 1 and 2. Not in the way she did when she made her chose Stefan in 3x22. She didn’t need his comfort or support anymore; she didn’t technically need Damon’s either, but she appreciated him being there because she talked and he listened. Elena Gilbert has moved on in more ways than one. She’s no longer the little, innocent girl who fell in love with Stefan; she’s a grown woman who’s free to do what she wants to do without needing anyone to help her do it.