It's never ok to hit a girl. Never. Not even if she cheats on you. A girl is not your property. She's a human being. She is just as important as you. Furthermore, she is your equal. And her wishes and feelings are just as valid as yours. All you can do is treat her nice, and hope she wants to be with you. If she chooses to be with you, great! If not, or if she chooses to leave you at some point, you have to let her go. You have no right to stop her. You don't own her, and you don't have the right to tell her what to do. She's your partner. Not your servant, not your sex slave, and not you're punching bag.

Sex and Crime: Oliver's Strange Journey