EDITED Exclusive FWB cheated... how to feel?

Hey guys! So I just found out my exclusive FWB cheated on me legit the day I moved off campus and back home. It wasn’t even a day. We weren’t dating. We wanted to but I told him we should wait til September to date because we have a pretty big distance (About 7 hours) and we wouldn’t see each other for s while. Well, some other girl jumped in his bed. A girl from our friend group. And I forgive her because she asked many times if me and him were exclusive and said that I said we could take a break for the summer. Which he misconstrued what I said. We had talked about being exclusive for the summer. We both agreed to. And then on Saturday we got into an argument because I relapsed (self harm) and he wants a break now. My friends think it’s the guilt catching up to him. I’m going to confront him but part of me is like, you weren’t even dating. You can still make it work. But part of me is like if he can’t even be exclusive FWB then how can we date? His last GF cheated on him and he was heart broken. I have never been in this situation and I don’t know what to do.

EDIT: he admitted it was cheating and that we were basically saying. (We didn’t want anyone to know so we went by FWB). Him and the girl have two different stories and he’s telling me the girl is psycho and trying to break us up. She’s saying he said it was ok they slept together. He’s saying he never said that and she insisted sec but he stopped it. She’s saying vise verse. There are so many different lies here. I’m honestly going to make a group chat between us three to figure this the fuck out and how to go from here .