He won't pretend it doesn't hurt.
His brother, the man he had spent four desperate months trying to get back, had just told him that he would hunt him. Dean would hunt him.
Once Dean had promised to kill him. He had promised but Sam had known that Dean would never do it. Dean protected Sam. It was his duty, his job, his reason for living. To Dean Family meant everything. To Dean Family meant sacrifice.
Yet now, now Dean wanted to hunt Sam.
It hurts more than the two punches that Dean had thrown at him. Not the first punches and probably not the last. He can taste the blood on his lips, feel his mouth swelling against his teeth but the pain is negligible, it is nothing compared to the look in Dean's eyes, the curve of his mouth, the bitter disappointment in his eyes.
Sam thought that the pain he felt after Dean's descent into hell was the most unbearable of his entire life. Worse than the pain he felt after dad, worse, even, than the pain he felt after Jess.
The pain he was feeling here and now was intense, thick in his throat like bile and wrapped around his heart like poison ivy. He felt as if he could cry forever and the hurt would not be erased. He kept swallowing the lump down but it wouldn't go, just stayed there, choking him, until he couldn't speak.
He wants, more than anything, to be Dean's little brother again. Wants the dependence he always felt, wants to need his brother, to hide behind Dean's broad back and let his big brother chase away the monsters that are always close by.
He wants that old 'bitch/jerk' relationship, the prank wars, the teasing, the Nair in his shampoo. He wants to tease Dean about the music in his car, about mullet rock and old leather. He wants to lie on the lumpy bed of an old motel room and watch cable, to watch 'Die Hard', 'The Simpson's' or even porn.
He knows that that isn't gonna happen. It can't, it won't, its impossible now. Dean told him that God, God doesn't want him to use his powers. It's been a while since Sam's prayed and he doesn't think he can even bring himself to pray now.
He slumps in the Impala and makes the words sound right. He swallows back the ball of pain that has become such a big part of him. The world passes by the window, dark and fathomless and Sam falls into it, falls into the dark, his brother taut and tense by his side.
Sam swore he wouldn't ever go dark side, swore he would never become like Ava, like Max. He wanted his brother to end it before that ever happened. He wanted his brother to do what he had done for all of Sam's God-forsaken life. He wanted Dean to protect him, he wanted to Dean to accept him; he wanted Dean to love him.
Once his life meant something but now all it does is it hurts.