C'mon let the kid live. You guys are clearly giving the more mature perspective but let him save some of his pride. This is high school, granted he is still under the age of 18 there will be no charges pressed, everyone will think he's cool and know not to fuck with him or his girl, and the kid stated WITH HIM.
If he doesn't fight (OP you always have the choice to fight or not), everyones gonna think he's a pussy. IE try to fuck his girl, try to fight him, what have you.
OP either fight or don't but get ready to fight. I have a feeling that either way, he's going to keep pushing you. No-one in high school is going to take the Mr. Clean and Bushy mature perspective, IT'S HIGH SCHOOL. Especially not this douchebag.