Hi!
I think it might be Crippled by Enchantress
Crippled Summary: One night, Buffy finds herself unable to cope with all the anger and pain within her anymore. She finds Spike and takes it all out on him in the most violent of ways. When the fight is over, she has the fire back. But when the brutal and undeniably one-sided fight is over, she realizes he's been really hurt. He's been crippled. She feels she owes him.. so Spike moves in with her, Willow, and Dawn. And everything in her life changes. Set during Season 6 sometime after Dead Things.