If his affair partner doesn’t want to be with him, if he was only a one-night-stand, it could be the reason he stays married. He simply doesn’t want to be alone, and staying married is currently the only option for him.
He has a person who cooks and cleans for him, and that’s enough for him for now. However, if another woman shows up in his life and wants to be with him, then he’ll most definitely leave his wife.