Jealousy problems. Help? Urgentttttt!?

[taydeee]

My boyfriend and I have hit a few speed bumps in our relationship. So much has happened and I will admit, I haven't been the greatest girlfriend on earth. In fact, I've been the worst girlfriend. I have never cheated on him, but he always accuses me of it because when we've broken up I've said some stuff like "I'm moving on with someone else" or something like that. He's done the same too, but not as much. He always says "I'm not cheating on you. If you treated any other guy like this, they would cheat" and he's also said "I wish that I was talking to other girls so when we break up I could be like to you, well yeah I'm moving on too" He hides the fact that we're in a relationship on facebook, although that isn't SUPER important. As I said, he's lied to me in the past so I don't have trust for him, however I'm giving him the chance to earn my trust back. But I cannot help but feel he is cheating on me with someone else. He talks to other girls, I'm not sure if he flirts with them or not, but yeah. He speaks to them nicer, ahah. I've always got the feeling that there is someone else and because of that it's taken a toll on our relationship. I don't know what to do anymore. He accuses me of cheating all the time, but he said that's only because of what I've said about other guys - that may be true but I've also heard that if someone accuses you of cheating, they're cheating themselves. I need opinions. How can I trust him? How can I let go of this and all my issues? Any opinions will do, I don't care how hurtful or whatever they are!
I'm scared he's going to cheat on me because of how I've been acting. I'm slowly changing though, and so is he. But I'm scared it's too late.