You need to get away from your perceived, fantasy world and look around you at the real one. She is hardly your girlfriend, and you have no business punching someone in the nose. There are better, adult ways to deal with insults and abuses.
Reminds me of that guy on Christmas Eve who showed up at his ex in-laws' party and was dressed in a Santa suit. He shot up the people there and burned down the house after shooting an 8 y/o girl in the face. He decided he had been abused by his ex-wife and was going to show all of them, yessiree bobtail.