*whispers* Sherlock doesn't don't enjoy fights. He hates stitches, dealing with the hassle of bandages, and having to clean up blood. Sherlock does enjoy the thrill of the chase and the mystery to solve but if he could skip the unnecessary pain of a fight that would be fine by him. He hates pulling bullets out of fresh skin and having to keep pressure on that spot until the stupid ambulance arrives. Most of all he HATES when he has to do this to the man he loves and not to himself.
Honestly, I think by the time Lily started her education at Hogwarts and her relationship with Petunia was getting worse and worse she projected her feelings on Snape, seeing him as a brother to fill the blank.