Should I be pissed off?

My ex and I break up and make up and one time we broke up he cheated on this girl with me I knew about her but he wouldn't tell me about her cuz he was afraid I wont speak to him again. SO now we hadn't talk to each other in a month because of our worst breakup ever and he had a girlfriend and this time i didn't even know about her and we weren't a couple but then we started talking again and do things so he cheated on this other girl with me and I feel so disgusted by him. I treated him wrong many times when we were going out and I should have got slapped because of how I treated him but now he's cheated on two girls with me and they just broke up. So what's wrong with him and should I even be mad at all?