HELP I'm so confused right now

So I started a relationship in October of 2015 with a great guy he was what every girl might want, but because of the heartbreak I had before him I didn't treat him that well and I used to break up with him a lot even though we'd still get back together. In April I broke up with him and didn't hear shit about him or know anything about him for like a whole month so when I see him at the end of May he comes to say hi and I'm so pissed because of it. But I can't do anything about it I can't just go back to him besides I started talking to someone else and then he disappeared again until the middle of June and I had engaged in another relationship but I realized that I'm in love with him and he had been persisting until he found out I had a boyfriend and then he stopped trying. But my current boyfriend has changed completely we barely talk anymore and I find myself arguing daily with my ex and we had sex three days ago I literally cheated something I hadn't done like ever. And he told me he loves me and now that I told him I was willing to go back he's all like no I don't want to I don't fucking understand. Can you guys give me any advice on what to do because I'm seriously into my ex I hadn't realized it's not like I don't care for my current boyfriend because when we do talk I forget cmepletely about my ex existing. I feel like I'm drowning.