"Next time he either has to fight me or call the school police."
Wow. Well, no doubt you're a young male.
Be a grown up, try to work out a compromise in an adult manner (set times you can listen, invite him to listen to how loud you play as someone else suggested, be a bloke about it). If you think he's being unreasonable, ask staff to mediate. If all else fails, realize you live in close quarters, not everyone is going to be happy, and sometimes that means it's YOU who isn't going to be happy. C'est la vie.
Get a good pair of headphones. Don't play them too loud, you don't want ringing in your ears or other hearing loss later on.