Do you think he was already sleeping with her?

I was dating this guy for a year. Then he just up and broke up with me. Friday night we were giggling and cuddling and having a great night. Saturday morning he wouldn't touch me. Saturday night he said "I can't do this anymore. I can't be the guy you need. This is over. I need time to work on me." Then he changed his mind and said it was because I wasn't communicating with him (I was). Then he said it was because he didn't love me anymore. Then he said it was because I didn't like his ex fiance. Well duh. He was always texting her. He would even meet up with her at her dorm and they would go out for drinks and then he'd come see me and say he was with "a friend." I knew though and if I pressed it he'd tell me he was with her having drinks. He would invite her over to his apartment and she would hang out with his roommates and friends and him. I wasn't ever invited and he made sure to do this when I was busy and couldn't just pop in. He didn't ever want me to meet her, he said it was because she didn't like new people. I would get pissed and we would fight about it. Then it would get dropped because "she's just a friend. She means nothing to me. There's a reason we broke off the engagement." Anywho. When he broke it off with me, he went and spent the night with her. I'm certain they had sex that night because of who they are. They're both super sexual people and have history. Do you think they were already sleeping together and the guilt finally got to him? He refuses to acknowledge that and just tells me to stay out of his life. But his ex fiance and I go to the same college so he's on campus all the time with her. He refuses to admit to anything. I told him the fact that he was telling me she didn't mean anything and then slept with her immediately made him as bad as a cheater and he didn't even respond. What do you think?

UPDATE: sent her a message asking her to just be honest with me and tell me if he cheated. She got super defensive saying it's none of my business. In other words, YES.

Then he texted me yelling at me for texting her. He said that he never loved me (lie to get me to leave him alone) (who asks someone they don't love to marry them and have their children?). So yeah, don't believe that. But then he said "I just didn't want to be like Z, that's why I broke it off after.." (Z is my ex who let me know he was cheating and then wanted to continue our relationship. I despise him. Everyone in my life despises him.) In other words, YES.

So. He cheated on me. Thanks anyways girls..