It was good of you not to flip out on her. Seems like a mature reaction on your part.
If I were you I would try to verify her story about the party by talking to someone else who was there. Is she trying to minimize or conceal her role about what happened?
She may be hesitant to get back with you because she doesn't know what she wants. My W had an EA and insisted that he was just a "friend" and a "nice guy" and I found out later that he had told her how he had feelings for her, etc. My W was similarly confused when we tried to R after me finding out about this and confronting her. Unlike you, though, I blew my stack, and after a few weeks of separation she wanted a D.
T 10 years, M 4 years, both 28 years old 7/3/2013 - W wanted D, we attempted to reconcile 7/20/2013 - discovered W's EA, attempted to reconcile 8/24/2013 - W told me she wanted D, filed papers
