Is our relationship even worth it anymore? How can I learn to trust him again?

I have been on and off with my boyfriend for two years now, we’ll call him Rich. I have always been very committed & faithful to him and yes I know that I probably should just move on and find someone knew but I’m in love with him and I want to make things work and as the moment is seems like he wants to, too. We first broke up because he was a very sexual person and it bothered me, so I told him unless he can cool it down a little bit and respect the fact that I don’t want to “fool around” all the time, then I couldn’t be with him.
We were apart for a little over a month, when he finally proved to me that he didn’t just want sex, that he wanted a meaningful relationship. We stayed together for a few months and then one morning he randomly stopped by and told me he couldn’t be with me. I was absolutely heartbroken, but we were talking and he apologized a lot, and I felt like giving him another chance. Well just so happens that the day we were supposed to hang out and talk things through, while I was waiting at home for him to text me, a get a text from someone saying he was with another girl, lets call her Mary, and had been all day and had been kissing on her and stuff like that. Later that night, I was talking to my best friend who is also good friends with him and she told me that she had heard that he had cheated on me with Mary, so I texted him and asked him about him kissing her earlier that day and he admitted to it and I asked him when else had he kissed her and he admitted that he had kissed her that night before we broke up and that’s why he ended things with me.
I was beyond mad and didn’t want anything to do with him, I wouldn’t talk to him for months and I started to see this other guy, we’ll call him Russ. I seen Russ almost everyday and Rich was very jealous and started dating Mary, well things ended with Russ and soon after things between Rich and Mary ended but Rich started talking to another girl, who we’ll call Katie. Rich ended up getting screwed over by Katie and so he ended up dating a few other people but nothing serious.
Homecoming came around and Rich asked me to go with him, just as friends, so I agreed, well of course when that night came around I remembered why I had fallen in love with him and two days later, we were finally back together. We were as happy as could be, or so I thought, I found out after about three weeks of being together that the whole time we were together he was still talking to Katie, everyday and flirting and telling her he missed her and stuff like that.
We ended up getting into a fight because I said that it made me uncomfortable when they hung out and he ended up making plans with her for the next day, just to prove to me that I didn’t control his life. We fought the whole next day at school, and by the end of the day we had broken up and he took her home and also went to a basketball game with her and had ended up making out with her. They ended up getting together but broke up soon and that’s when he came back to me, we were together for about a week when he broke up with me and got back together with her, they broke up after a few days and then that night he texted me saying that he wanted to try to make things work and of course I agreed, the next day during school, he text me saying that he was going back to Katie. I, of course was upset once again.
I tried for so long to get over him and just couldn’t and it got to the point of me cutting myself. But prom time came around and I just went with a bunch of my friends and Rich ended up getting very jealous seeing me dance with other guys, at that point I didn’t care, I danced with a bunch of different guys and then at after prom, one of his friends, he’ll be Joe, kissed me and I went along with it. The next day I wake up with all these texts from Rich telling me that he had hated seeing me with other guys and had broke up with Katie to be with me, but after Joe had kissed me, I was curious to see what would happen.
Me and Joe started to hang out and being a naive girl, I ended up sleeping with him, it only happend about 4 or 5 times Rich was trying to get back with me the whole time that me and Joe were seeing each other. Well things with Joe didn’t end up working and a few weeks later I was at a party and for the first time drank, I got extremely drunk, I don’t remember anything but I guess I slept with another one of Rich’s friends, who will be called Zack. Me and Zack decided it was best if we didn’t continue anything further.
Rich knew nothing about Joe or Zack and was trying to get me back and later he found out but told me that he didn’t care and wouldn’t let it bother him if he got me back, we ended up getting back together but he throws it in my face a lot that I did that and I just found out that he’s been talkin and seeing Katie again. I don’t see why he’s mad at me for Joe and Zack when we weren’t together when they happened but it’s alright for him to talk to and see his ex girlfriend, makes no sense to me.
But he’s having a party this friday and a lot of girls are coming. I’m really worried that something might happen with one of them.

I don’t know what to do, I want to be with him but I can’t continue to be with him if I can’t trust him.