Obviously break up with him. Leave and then help other women in abusive relationships. It would take awhile for me to want to be in a relationship but eventually I'll find a good one and show the abusive douche how a man should act
Walk away. Actually not long after a friend of mine had gotten out of an abusive relationship I gave the following warning to whomever I dated. "If you ever hit me, make sure I go down and stay down. If I come back up you ARE going down. If I don't get back you better leave town, because my family and friends will hurt you."
I would recommend you call the authorities first and then break up with him or her and once the authorities is there is a good time to break up with that person plus you will feel much safer with the authorities there and then tell a trusted adult but either way there gonna call the authorities so i would just call them and block that person from everything and avoid contact and leave it at that