Instead of second-guessing communicate and ask him directly to his face if he wants to break up. Second-guessing only gets you into trouble. By communicating you may find he has some personal problems that he can't seem to resolve and it may not be all about you.
Here are some signs:
These are but a few, but as I said ask him right to his face. Tell him you don't play games and if he doesn't love you enough to stick it out with you then you want to know now. This strengthens your own character and gains respect by others as you being a 'straight no nonsense kind of woman.'