ahhhhh sorry but i gotta rant. I don't get putting this kind of thing in cheating games, and imo it ruins them.
As soon as the story takes this direction, it completely mutes the cheating aspect. If a person feels justified, or like they have the 'right' (and whether it can or can't be said they reasonably do is beside the point), then there's nothing taboo, or naughty, or even particularly slutty about it anymore. The guy keeps ignoring his wife and spending time with some other woman. What do you expect to happen. It's no longer 'wrong', it's no longer the forbidden fruit, it's just a normal and completely predictable development.
Cheating fiction shouldn't be about the breakdown of a shitty relationship, it should be about the allure of the forbidden, and how it can feel good to be bad.