Ah ha ha ha ha ha, it's Rashomon in Gryffindor form! Omigod, I LOVED this! The voices are amazing, and it's the details that make it particularly funny and fabulous, but it's also one of the hottest things I've read!
Funny--The repetitions in the detentions and the deviations thereof! (I will not flood the corridor--that was PETER) (Hairpin hairpin hairpin bowtruckle) (Order of Merlin) Peter and the invisibility cloak! "Boils or spots?" Gryffindor's Fourth Marriage! Pumpkin rogering! Multicolored glow-in-the-dark mustache! McGonagall shouting so loudly at Sirius they're afraid she's going to pull something! A face like a nogtail's backside! "And you'd just better." The drunken slurring!
Hot--submissive (slutty!) Remus! "Kits off, now." The arguments over who's got whose hand on what!
And both ways, FABULOUS.
And I particularly love how you didn't ignore Peter in this--he played his part even if he didn't get into the threesome, and then he has that lovely, almost chilling coda at the end. Awesome, just awesome story.