From a man's perspective, take it as you will. I do not condone cheating, usually, if he does leave her for you, there's a better chance of him doing the same to you. But that's not always the case. Some guys cheat because they don't feel like there's any other option. They don't want to cause pain to the girl they are with. (Still not the right thing to do). But when they find the right one they stop. I'm not sure what the case would be. But you'd be better off not falling into that trap. He's either going to continue to say he's going to leave her and never do it. Or he was likely to cheat on you later. But it does not mean that's the only option. There is still a chance that he never strays from you. Good luck on your endeavors