OOHhhhh nice. I'd read this one back in May because of the Watersports. Couldn't resist reading the kink. So wonderful here! Guh! I love their dialogue and your description:
“No…” Severus moaned. “I can’t…it’s coming” Remus planted his feet and pointed Severus’ cock directly at his own. Severus started to piss. Remus directed the stream with one hand and pumped his cock frantically with the other. “So good, so hot,…aahhh, Oh, Severus, more” Severus’ hips jerked as the piss that had been contained too long sprayed out of him. “Can’t stop.” Oh SO good indeed.