hey, i m in the same situation with my bf!!! you have to try gaining trust again. maybe he really doesn't have anyone else, but just wants to play single coz of some of his complexes. if u really wanted to leave him you would have done it already, so it means you too are pretty much involved into this. so you only have 2 ways, either closing the door behind him and never let him in you life again ever, or working on rebuilding your relationship and gaining trust back.