bad relationship

so I've been in an exclusive relationship with a guy since I got to college and I just couldn't help but to really care for him. When I first met him he was so nice and genuine and I trusted him so much. We click so well that it felt right. However, things started to get a little weird when he joined a frat because he started to get into drugs and was trying too hard to fit in. Although, we continued to do our thing and he opened up to me about everything and told me that I mean the most to him out of all the people he's met and how he wants to be exclusive. However, he started acting weird about how I was "too friendly" even though we have all the same friends who most I've known longer than him and would make me feel as if I was doing something wrong every time I talked to someone of the opposite sex even in public or group settings. Being a girl who has always had a lot of guy friends it was hard for me to ditch my friends for him so I didn't but I tried to be respectful on the environment in which I saw them. He, on the other hand, had tons of girl friends one of them he was even a thing with before me. He also would never talk to me around our friends which was weird because everyone knew about us and would even ask about us but if I ever mentioned it he would yell at me and tell me it's my fault because I'm "too friendly" so he expects me to just stand and not talk unless he is with me and that I was crazy for bringing it up to him since he isn't doing anything wrong. We had gotten into a fight 2 days before Halloween and at the party was grinding on the girl he was a thing with before me the whole time right in front of me so after the party we talked about it and somehow he made it my fault and I ended up apologizing again even though he's the one who messed up. I started to see that I was in a bad relationship so I started to pull back a bit but then he started acting like he really cared about me. So of course I gave back in. Although the girl he was with before me had asked him to her semi and he said yes as friends. Of course, it bothered me deep down because of the recent history but I didn't want to seem "crazy" so I went along with it and decided that I trusted him. So the morning of the semi he came over and was telling me about how I mean so much to him and how I know him better than anyone else here and had sex with me. BUT that night he took the other girl home after semi and had sex with her and posted about how she was the "most beautiful girl" on social media. So I texted him, obviously, and he never responded so I blocked his social media and decided it wasn't good for me. However, I just can't understand how someone could go from saying how much I mean to them to purposely trying to hurt me. He never even tried to defend himself or say sorry.. it's been a few weeks now and I'm trying really hard but I'm very hurt and as much as I know he's not good for me I can't help but to want him still which makes me so upset because he made me feel awful about myself everyday. I can't even look in the mirror without crying or feeling ugly. Ive kept it together in public because I see him everywhere so I try to act like I'm happy and not hurt but I'm broken and don't understand why he would go out of his way to hurt me like that. I hate the fact that he never even looked back to make sure I'm okay or texted me back. I just have no closure.