A guy grabbed my girlfriends ***?

This guy i have been in fights with in primary school has been giving me **** again lately- I'd have thought he would have gotten over it after all these years yet, he hasn't. Today me and my girlfriend were walking down the corridor to Biology, when he reached out and grabbed my girlfriends ****. I saw it out of the corner of my eye, swung around and punched him fair in the face. Now I've been suspended for 2 weeks and he has a broken nose. I don't find this fair i was the one who got suspended for protecting my girlfriend, yet he got in no trouble for violating her.. What can i do about this? He doesn't give up.