He was abused as a child. He has also has gotten beat up a lot. He's tough and can defend himself but he's not in a good state of mind, until he met you. You're his reason to live. You two started dating and he always come to you for comfort. that's when you vowed to yourself to protect him no matter what

One day you see him fighting some people, he's losing badly and you run over and stand Infront of him