So, two things.
1) Why did they randomly throw in a shot of Damon and Kelly Donovan from "There Goes the Neighborhood" in there? I looked at it bunches of times to see if maybe I was wrong and it's a new character, but no, that's totally Kelly (Melinda Clarke) from that episode with Damon, Kelly and Jenna at the bar. That was just weird.
2) I had pretty much convinced myself the Stefan/Katherine stuff is some dream of a kind (maybe Kat putting it in his head), but there's a moment where she's clearly looking at someone and smirking her ass off that said someone is seeing Stefan going all wildly passionate with her. I don't think it's Elena, but I could see it being Damon -- who'd be there to update Stefan, bring him blood. But the point is the fact that we actually see Katherine looking at someone like that, why would she do that in a forced dream on Stefan? And that makes me lean towards the idea it's real; and if so ... can I just say whoah? I can't really see Elena not being majorly (and I mean MAJORLY) affected by Stefan getting all hot and bothered with Katherine due to the fact that ...
(a) they look alike
(b) was there before Elena, and was the reason he started
(c) Katherine is a huge part of their problems now
(d) bitch caused Jenna to stab herself in the stomach
(e) bitch snacked on Jeremy
(f) after only a few days, he's giving in already which shows that, yeah, he's been lying to Elena and himself that there are and have been feelings still there
I'm not trying to say it's so much worse than what Damon did (you know, the whole neck-snapping of her brother), but they're terrible in different ways, and because it's about the heart, Jeremy didn't die, Damon wasn't trying to take him from her, but rather turn him and there were extenuating circumstances (GAWD! I am SUCH a Damon stan!), this could hit Elena as a deeper betrayal. Still, she's clearly forgiven Damon for what he did (even if she hasn't said it), so I can't see her not forgiving Stefan. On the other hand, I can't see her easily stepping back into a relationship with Stefan either for quite some time.
So, yeah. It will be very interesting to see how this plays out.