I was with you until the second to last paragraph. He is a jerk. The dude has a "problem" with some shyt that has always been there. Like how is that fair? If this shyt was the other way around and he had a few extra pounds and he kept asking what's wrong and she said "Well you said you would lose weight and b/c you haven't I was thinking about cheating on you." This would be a WHOLE different conversation.
You'd all probably tell him to leave b/c she can't be trusted. You don't threaten people with cheating. That shyt is hurtful, builds resentment and leaves a lasting impression. She may not have said anything but that shyt probably cut deep. I doubt she'll lose the weight and b/c of that the fact that he told her he wants to cheat will always be in the back of her mind. I agree that he played himself.
Dude said if you continue to look exactly the way you did when I met you I will cheat on you. But let a woman look at another man and half of ya'll would die a million deaths and question ya stroke game.