Been years since I seen this movie, I'm not going to excuse the actions of Joe Torry's character, but he'd kinda left her alone after she started ethering him hard.
When he started brushing his hair and shyt and she was talking about his weak azz fade he had kinda conceded defeat then she had to take it there with that's why I'm cheating on you.
He shouldn't have put his hands on her and controlled his emotions, but she also should have known when to shut the fukk up too. When tension is high you don't further agitate a situation by rubbing some shyt like that in someone's face.
I don't agree with Pac's character leaving him either.