Coping with feelings of betrayal

I've been broken up for about two months now (dumpee). I'm at a university where she's also studying. Back when we were dating, I brought up a guy with whom I was uncomfortable because I thought he liked her, they had the same classes and obviously spent time together (her program's setup is like that). What I didn't bring up is that I think she also has a thing for the guy. Fast forward, she decided to end things because I was asking for too much, when I was just asking to spend some time with her (literally stonewalled and ignored for day/s).

Now I kept seeing her with the guy I told her about. The guy was obviously waiting for her because he didn't have any classes left. She was all smiles and happy when they were talking, similar to what I saw before. It resurfaced wounds that I thought were already healing well. I cried and cried because my gut was right.

How do you deal with this situation? I can't completely go no contact because I keep seeing them.