ok, so i have read over this like three time just to get the situation in my head!!!
Firstly, you need to find out how this relationship with the other guy ended? To me it sounds like she is scared to commit for two reasons:
Reason number 1: this guy she was with after you seriously screwed her over and betrayed her trust or something along those lines. She's scared to open her heart back up to you - even though she knows you- but once you get burned it's hard to trust.
Reason number 2: she never got over you. she thinks that breaking up with you in the first place was a big mistake and she went out with this other guy for a cover and she feels as though she hurt you and doesn't want to hurt you again because she feels like a bad person. The whole situation where she called you a jerk...maybe she was hiding the way she really feels.
You need to show her that you can trust her again. Girls are silly and over think things way to much (trust me i'm so guilty of this!). So lets go back to the old fashion way of things. TALK TO HER!!!!!!!!!!!!! take her out for dinner or go somewhere casual and TALK TALK TALK!!!
Once you have spoken about things go from there, tell her how you feel and put the ball in her court. Once you have said your piece you'll feel better and if things work out for you two that's great!!! If not then you know where you stand and you would have heard it from her not any one else and you can move on...
Hope this helps!!