Did I really mess up here? Help please..

Hey guys, I really wanted to get some people's opinions on my relationship issue at the moment. My girl and I have been together for over 3 years now. Things were great most of the time, but a few months ago things started to change. We were commuting together in the mornings and took the same train everyday. Gradually throughout the semester we would get in ridiculous fights that she would start. Fights that I couldn't even believe we were in. Finally after a few months of it, the truth came out. She told me about how I have been staring at some girl non stop everyday and how pissed off she is at me. (she's just been holding it in for 3 months). I asked her who this person I am staring at is, and she made me guess. She wouldn't tell me until I guessed the person. After some time, I put 2 and 2 together, (the one place we are at consistently, and the same chick is there) and I guessed right. After that fight, I have never seen her so mad at me. I thought she was going to have some kind of mental breakdown. I apologized a thousand times and told her how I never meant to hurt her. Here's the thing...yes I may have looked at this chick from time to time. But I swear I never "stared" at her, or looked at her disrespectfully. None of that. I then asked my friends who took the train with us, and they both said I never disrespectfully stare at her. I clearly remember most of the time I talk to people or read my paper. (wow, sorry this is kinda long). So, we finally were able to move past this. However, about 3 weeks ago the fighting started up again. She started acting not like herself, and I could tell something is wrong. Last night she tells me that the reason she is always so mad, and sad, and depressed is something from the past. That something, is that chick we got in a fight over a few months ago. She tells me how she hasn't gotten over how much I hurt her, and she can't even regain her confidence back. She tells me that she has such a hard time believing me when I tell her how beautiful she is or how sexy she is to me. She says she cant get over the fact that I knew exactly who the person was when she claimed I was staring at someone. I told her I guessed, because she wouldn't tell me who! Anyway, I have never seen our relationship this bad and I cant take any more of this. Helpppp! :upset:

From my own personal experience it seems like she is over reacting, I think every man under the sun will check someone else out from time to time it is natural. It sounds like this is just the tip of the ice berg she may have self esteem issues or it might be something else. If it was me id buy her some nice clothes, take her out for a meal. Make her feel like shes the centre of my universe then sit down sometime after and try an discuss how shes feeling and why?