The first time he uses his powers he ends up with a headache so bad it makes him vomit.
He stays in the motel room for a whole day, throwing up into a trashcan, too tired, too weak to even get to the toilet.
She sits in the corner and watches him, all dark eyes and sad drooping mouth. She isn't the smart ass blonde he knew anymore but she is still obsessed with him learning and he does it because he doesn't have any more hope left.
The next few times become easier and he gets to feel proud of what he has achieved. It is like a steep learning curve, like what he used to do at Stanford, taking things a little step at a time.
He is saving people, hunting things – the family business – trouble is, he hasn't a family anymore. He is an orphan, motherless, fatherless and, now, brother less and his only friend is a demon chick who is possessing an innocent and messing with his head.
He doesn't touch her but he knows that she wants him to. He can feel her watching him in their darkened motel rooms; feel her sloe eyes on him when he comes dripping out of the shower in only a towel. He feels it sometimes, the tightening of his jeans, the tensing of his thighs. He ignores it, goes back to his good right hand. The only important thing here is his lessons, lessons he wants to, needs to learn.
He watches the man vomit black smoke from his mouth and he smiles, proudly. The headaches are long gone and he can feel the power flooding through his veins like the demon blood that put them there. He remembers Ava and Jake talking about flicking switches and he understands.
He isn't doing this for old 'yellow eyes' though, he is doing it for himself, he is using his powers for good.
Dean comes out of the shadows and Sam freezes. There is a long, long silence and he knows, deep within his soul, that Dean is fucking mad. He knows that look, knows the set of that mouth, the cold jade of those eyes.
The punches hurt more than the headaches did and he wants to rip off his ears when Dean tells him he would hunt him.
It is easy, in the end, to lean his hot face against that cold, familiar window and give in. He says he is done and he means it, then. His brother smiles, says thanks and Sam wants to cry.
He tells Dean to sit on the bed and stay where he is. He tells Dean not to worry, to go to sleep, that he will be back soon.
Another day, another power and he hot-wires the car with intricate precision, driving to another warehouse, another demon, another exorcism.
Ruby looks proud, like a mother hen with her chick. The guy survives and Sam should be ecstatic. He feels everything now, feels the power inside of him burning through his veins like fire and he stretches up his arms, the beat and throb of his heart loud and heavy in his ears.
He feels instant guilt when he slips into his bed. His brother is asleep opposite him, his expression peaceful. Sam stares at that familiar face and swears to anyone who is listening that he cannot, will not do this again.
Sam knows that he is lying, as much to himself as anyone else.
He knows that, ultimately, his powers will become so great that Dean will not be able to stop them.
Problem is – neither will Sam.