Feeling betrayed

I've been in a relationship with someone for 7 years. Four months ago, we hit a bump in our relationship and I was partially at fault, and so was she, but I feel that what I've done should be enough to at least begin to mend the pain that I caused, and I've already accepted the fact that I made a mistake, and I wanted to do everything i could to show that I was deeply sorry.

A basic rundown of the problem is that it started to get to a point where I felt that I could not breathe, I couldn't do things I wanted to do and felt like I was being held, and squeezed too tight, and so I broke it off with the person for a few weeks, but in that time, I was talking to a friend, and she was just that, a friend, who happened to be in one of my college classes. We talked, and the person whom I was involved with saw it as more than just that we were talking and just friends.

So I admit that this could've been avoided if I hadn't start talking to this person around the time I suggested that we take a break. And because of that, i felt that i had hurt her, but in the time I spent away from her, I realized how much she really meant to me, and that has been my goal ever since we got back together, showing her just that.

She's normally a vengeful person, and I never really thought she had it in her to do what she has done now. After we got back together, things were going well at first, but then something happened to my car, which was my only means to go and see her. I decided to fix the problem myself which took about 3 weeks, and during that time, I noticed a change in her, a dramatic change, and it was then that I began to get a gut feeling, an instinct that there's was something going on, and I knew there was or else she would not have changed this way.

I pleaded with her, and every time I asked, she would say that there wasn't anything going on. But what happened during the 3 weeks it took me to fix my car, she started talking to someone else, and months later, things may have progressed between them, but not to the point where she slept with him, at least I hope not.

After the many times I asked, and she told me no, a couple months after she became involved with this person and started going out on dates with him, there was one time something happened that she did not expect. They went to a restaurant to eat, and by luck would have it, one of my good friends was there to witness it, and she knows this person and she knew that he had seen her there.

Feeling bad for me, my friend decided to tell me what had happened and it was then that I felt the worst pain I'd ever felt, to be betrayed by the person you have so much love for.

She claims that she still loves me, and that she will break it off with this person, but from my perspective, thus far, that doesn't seem to be the case, and now she wants to have a break, but knowing that she will be spending time with this person, this is something I see as unacceptable. And so now, I'm torn as to what to do. Do I wait and try to get her back, or do I forget and try to move on. Trust me, I've tried moving on and at this point, it's something I see as an impossible feat.