Elena has been consciously attracted to Damon since at least the time of the Miss Mystic Falls dance. She was devoted to Stefan, but she was not immune to Damon's charms, and who would be? During Stefan's absence, Damon grew stronger, saner, and ever more dependable. And while he didn't throw himself at her, he has made it patently clear he is deeply in love with her. Oops. I used the "in love" term. Well, okay, I mostly want to avoid it when assessing Elena's feelings; that's where I find it the cloudiest, because it's clear (to me) she has feelings for both brothers.
Elena's not stupid, you know? She tried romance with one vampire, a seemingly good one, only to watch it go all to hell. Now here she is, developing deeper feelings for Damon, but she knows what he was when he first came to town. She knows of (some of) his kills. She knows how mercurial he can be. I mean, he killed Jeremy, for pity's sake. She also is painfully aware that he is the brother for whom Stefan sacrificed their love, and his own character, if not technically his own life. She is struggling with, in my opinion, whether it is wise to get involved with Damon, and, whether getting involved with Damon would be the ultimate betrayal. Were Damon the more patient type, Elena might be content to let the question of their romance simmer on the back-burner, for years to come. And? I don't blame her. She is 18.
Now, one E/D fan said that she feels, that in the porch scene between Elena and Stefan, Elena lost a lot of the growth she earned this season. That wasn't my opinion after watching once, but each time I've watched that scene since, I've cringed for Elena. I think my friend is right about that. It is sad to see Elena so desperately seeking an emotional response from Stefan. But I'm still not sure Elena is doing so, as a romantic partner, so much as she is pulling out all the stops, to try to break through to Stefan's better angels. Have you ever gone out for dinner or drinks, alone, with a recent ex? Even when you know, intellectually, that you don't want to get back together with the ex, it can be difficult not to treat and talk to that ex as if he/she is still your sweetheart. That's how you're used to *being* when you're together. You have to learn a whole new way to be. It takes time, and distance.