Sooooo.... Im sorry for this super long rant but i need to just get it out

I was dating this guy and he has a reputation for cheating and generally does not have long relationships but he has liked me for a long time and I liked him too. He dated this girl on and off every couple of weeks for about a year but broke up with her so he could ask me out. He did and it was great. I rlly though he liked me and I was actually happy for the first time since me ex broke up with me which was the start of last year. But tonight I'm at a sleepover with the girl he dated on and off and a couple of other friends and we started talking about him. A few of the girls said that he asked them out while we were dating and I didn't rlly believe them cuz everyone at my school is obsessed with drama until they showed me messages. I broke up with him on the phone and explained over text y and he literally just said okay, fine, bye. I've been trying to play it cool and like I don't care but I rlly feel bad and disappointed in him and me. Him because he cheated on me with least 3 girls and I rlly did trust him for some stupid reason. I was rlly unsure at first to date him cuz I was afraid o was gonna just end up like the girl he was on and off with and he promised me I wouldn't be and that she was just a distraction. And I'm disappointed in me cuz I believed him and im usually so much better than this but I wasn't this time and I hate myself for it. I don't know why I feel like this and i like feeling like this and I don't want to feel like this. Can somebody help me?