I'm really sorry you're having such a tough time and for the pain you must be going through. Basically you have 2 choices. (1) Stay with him and accept that he is a cheater (I seriously doubt he will change) (2) Decide to leave the relationship and look for someone who loves, respects and cherishes you. Neither option is right or wrong. It's kind of a choice between short term pain (ending it now) and long term pain (always wondering or finding out he's cheating). Only you know what is in your best interest. Has he always cheated on you throughout the 4 year relationship? That might be something to explore. If it's a current thing...why? If it's gone on all this time...he has a weakness and/or bad character and is not likely to change. Good luck and best wishes with whatever you decide.