Damon is the bad boy, he attracts you, he pulls you to a huge abyss and makes you question everything. Stefen is the gentlman, he protects you, he puts you in a safe world and makes you a holy girl. You can do whatever bad things you want when you are with Damon, but you are supposed to be the best yourself when with Stefen. Stefen do everything that he could to protect Elena to grow up in a reasonable way. Damon just loves her whoever she becomes. Because of the sire bond, when firstly E said she loved D. I thought how wonderful true love was, it can be waited, it can be moved, it can be changed. While, all because of the fuck sire bond. She lived in a way that Damon wanted she to be.
Season 4 episode 23. They became WE. Damon is so selfish that he'd rather die than be human. He thought he made bad choices that hurt Elena. "I'd rather die than spend a handful of years with you only to lose you when I'm too old and sick and misrable, and you're still you. I'd rather die right now than spend my last final years remembering how good I had it and how happy I was, because that's who I am. Elena, and I'm not gonna change. And there's no apology in the world that emompasses all the reasons that I'm wrong for you."
E: Fine. Then I am not sorry either. I'm not sorry that I met you. I'm not sorry that knowing you has made me question everything. And that in death you're the one that made me feel most alive. You've been a terrible person. You made all the wrong choices and of all the choices that I have made, this will prove to be the worst one. But I am not sorry that I'm in love with you. I love you, Damon.