RUB A DUB

It's been a few weeks now. Remus hears them every fucking night, and he can't stand it anymore. Well he doesn't hear them usually because of the silencing spell, but he knows they're here, every night, fucking in his dorm. He knows it because he smells them. He smells sweat and sex, and that's the worst thing ever. He hears her walk in every night around eleven thirty, go to his bed, and cast the silencing spell. They could have a bit of modesty and do it somewhere else, where there's not other people sleeping for god's sake.
At first he was surprised when they started dating. He was friends with Mary long before Sirius even knew her name, so he'd thought she'd have told him. But he'd started realize there wasn't much between them, except for their night meetings. A group of first year had surprised them in an embarrassing situation and decided to tell the whole Gryffindor common room that Sirius Black had a girlfriend. They didn't want to tell the truth, that they were only "fuck-buddies", so they played along with it.

Or how Sirius and Remus got together in 5th year, after a series of unexpected events.

Title from the song RUB A DUB by Fauve