She doesn't mean to, Buffy knows.

It's her fault. She shouldn't have made her angry.

If Buffy would learn to behave, Faith wouldn't have to hit her all the time.

It's for Buffy's own good, always has been. The first punch to the last beating.

They don't know anything, Willow, Giles, anybody. They only see the bruises. They don't see how Buffy does stupid things like dancing with boys like Xander and taking on vampires by herself, so that Faith needs to punish her, because it's the only she'll learn. And it's all because Faith loves her.

All the whip lines, bruises, cuts, all the broken bones, they're all because she loves her.