Breakup Help Please

My boyfriend of 2.5 years has broken up with me after I found out he has been snap chatting another female from work on a daily basis and has been hiding it from me. He claims there is nothing going on between them but he has cheated on me before. He claims that he just doesn't feel the same anymore, but just a few months ago he said we were the best we've ever been. That can't just change in a matter of a month. We have suffered from him having a commitment phobia our entire relationship, so I believe that has a lot to do with this. But he won't listen to that. He has broken up with me before and always comes back. He says that won't happen this time. That it's just time to move on. And I don't understand why things changed so drastically. I don't know what to do. We live together and he says he is going to move out. I don't want him to move out. I just want him to give this a chance to work itself out like it always does. I don't know what to do or how to make him see that. I am so depressed that I just want to be dead. I feel like I don't matter and I'm invisible and nobody cares. I feel like everyone keeps abandoning me.