Confused about a girl

I had been seeing this girl for about a month and we really seemed to hit it off. We would text and video chat with each other about 17 hours a day and I really started to think that she liked me and I her. Please bare with me..
So, we would talk for hours and we seemed to have a lot in common with each other. Then we went on a trip with about 12 other people to Boston for a weekend and that is where we started to get more involved with our "relationship." In other words we kissed and she said she really liked me and I said it back to her and this went on for about 2 weeks until school started back up. We would still talk, but she seemed to be a bit off and when I would ask her if she was okay, she said yes and then she would stop texting me for the night. There were some good days and some bad days. Then she stopped texting me in an entirety and she was always the one messaging me not I. So I started to text her and all she gave me were one word answers and I was really confused by her behavior because I hadn't been in a relationship and it was weird. Then she told me she wanted to be friends and then we were. Then the next day, I found out she was seeing another guy behind my back and this guy was one of my best friends and we had a big fight and she stopped even acknowledging my existence. 2 or so weeks after that, she broke up with this guy and she told me she was sorry, but what I couldnt understand was why she was doing this now and not when she was sneaking around with my best friend. Then we started hanging out as friends again and thought everything was okay. We sat on the couch and talked for hours on end with each other and she seemed to be getting better. And was I wrong. But then out of nowhere, she stopped talking to me again and I don't know what to do here. I see her everyday and she doesn't even talk to me in public nor texting..did I do something wrong? If so, what should I do to help get her talking to me again?

Nothing man, nothing. This girl is treating you like crap and you're taking it. Don't talk to her again, have some self respect and cut this shit out right here, no more texts or calls, just silence. You're better off without her, you don't see it yet, but once your feelings cool off, you'll understand.

some girls have short-temper..

and there is the famous 'PMS' effect which might be the reason?

;)