Harry/Snape. "Every other sin that a man commits is outside the body, but the immoral man sins against his own body." (challenge by gmth)
"What the hell was in that?" Harry took the goblet from Snape's unresisting left hand, sniffed. "Aconite. Jesus."
"It's not your business."
"The fuck it's not. How long have you been doing this?" Harry was already on his way to the workbench.
"Leave that." Snape's voice was a rasp, had none of its usual command--which might have stopped Harry under other circumstances.
Harry had picked out the jar in just a moment of searching. "This is almost empty. How much of it are you up to? Does Dumbledore know?"
"Dumbledore has more to worry about that my methods of pain relief."
"You still didn't answer my question. How long?"
Silence. Then: "Since his resurrection."
"Fuck." Harry had his hands on the table, as if he knees would buckle otherwise. "And aconite is the only thing that helps."
Harry looked sideways at him. "No, you don't. Tell me. What else?"
Snape's lips were pursed, but it was clear he hadn't the fight in him tonight. "Orgasm."
"Wouldn't--er--wouldn't that be--easier? Than aconite?" He flushed harder.
The purse of Snape's lips...thinned. "The limb that the pain renders ineffective, you idiot, is my arm."
Harry couldn't flush any harder. So all he said was, "Oh." He dropped his gaze to the worktable.
He kept it there as he said, "Could I...suggest something?"
Three nights later, Snape was doing rather better. And the level in the aconite jar had remained steady.