Revenge wasn't something Sam started out wanting, but it quickly became the only thing.
It was the thing he woke up with and the thing he went to bed with at night. It was what he lived on until Ruby pushed food at him and reminded him that he was still human, stupid, and that he had to live on something besides blood and alcohol. He growled at her and shouted at her, punched walls. Threw things, hoping to break something – the room, her, himself. Anything.
He wanted it all broken, because it was broken.
He hurt in a way that it shouldn't have been possible to hurt, and he screamed into his fist rather than let himself feel the extent of it, burying it instead under layers of rage and self-hate, determined that he didn't deserve to feel anything because it couldn't compare to whatever Hell Dean was going through.
Ruby shook her head at him and used his shame as a weapon (as a tool), putting words to his own half-formed thoughts that always started with pathetic and ended with undeserving.
"Look at yourself," she said scornfully. "You think this is what Dean wanted? When his last words to you were to keep fighting, Sam?"
It drove the hurt deep until it throbbed in time with his own heartbeat, entwined into his soul like an unrelenting blackness, indistinguishable from himself. And when he pushed Ruby hard against the wall so that her head cracked and her mouth broke into a wide, pleased smile under his lips, he squeezed his eyes shut and let the growing blackness block out everything else.
He could feel her heart racing under his chest, the way he had her pinned against the mattress with her arm held out over her head and the knife poised to make the cut, and God, he wanted this. He hated it and wanted it so bad, and it was wrong, so wrong, but so many things were wrong now and he couldn't quite bring himself to care.
His hand wasn't shaking, he lied to himself. And if it was, it wasn't because of this.
"Do it," she whispered, and he felt himself tipping over the edge of a cliff, giving himself over to the blackness and hate and freak-monster-wrong-evil thing inside of him. It didn't matter, nothing mattered. Dean was gone, and he had to fight back. This was fighting. It was power.
He heard her gasp as the knife drew blood, felt her body arch up against his, and he gave himself over to it, responding with pure want and need, taking everything from her that she was willing to give and still demanding more.
"Sam!" she gasped finally, pushing him back and away, but she was pleased, he could see it, the way she looked at him. He wasn't sure why it made his skin crawl, made him want to throw up. As if he had just been violated in the worst possible way.
He wanted this, he told himself. Wanted her. Wanted this. Or if that wasn't exactly true, at least it was a means to an end.