Not Broken, Just Bent (слэш)

Written for this prompt at the kink meme: S7 (or any other time you want to posit with Sam plagued by Hallucifer). Sam needs pain to crowd the Devil to the back of his mind. Lots of pain. More pain than his brother is willing to dish out--or, at least, a hell of a lot more than Sam is willing to ask of him.
When the urges get too bad or his mind gets too noisy, Sam finds someone who can do it for him. He makes cursory efforts to screen these people, but their life is hectic (understatement) and as his mind turns on itself, he grows reckless. Dean knows nothing about it.
One day, he lets a dom tie him up and whip/cane him, knows it's dangerous but just doesn't care, but the person (man or woman) is really just a sadist without much skill or self-restraint, and they do serious damage. They keep on doing it. Sam never stops them, first drunk on the pain even if he rationally knows it's gone too far, then lost in his own mind, and the dom keeps going long after Sam checks out.
Dean goes looking for his MIA little brother and walks right in on this travesty of a "scene."
Dealer's choice what happens to the "dom" who tortures Sam. Murder not objected to.