To the world, Sirius Black hated Severus Snape.

It was easy, expected, even. Gryffindor versus Slytherin. Bloodlines. Houses. History. All Sirius had to do was taunt and the others would laugh, all teeth and cruelty. A well-placed jinx in the corridor, a nasty nickname in front of the class, ink poured over homework. It was tradition by now. A game no one questioned.

But when the lights went out and the castle fell asleep, Sirius would slip away from the dormitory and knock—just once on the abandoned classroom he knew Severus would be in.

And, Severus would always open it.

There were no words at first. Just hands, mouths, the desperate press of something they couldn't name. Sirius kissed like he was drowning, like Severus was the only breath he’d ever get. Severus never said “stay,” but he never told him to leave either.

And afterward, when their skin was cooling and the silence started to ache, that’s when Sirius would speak.

“I didn’t mean it. The hex. The name. What I said in Charms.”

Every night a new apology. Every night the same sin.

Severus never asked him to stop, and that was the cruelest part of all.

Because Sirius was addicted to the act. The secrecy. The pain. He wanted Severus like fire wanted oxygen. Destructively, needfully. But in the daylight, he was still James’s best mate, still the reckless heir to the House of Black, still too much a coward to tell the truth.

So he kept hurting him.

And kept trying to make up for it with kisses and bruised lips behind stone walls.

But Severus wasn't stupid.

One night, as Sirius whispered another string of breathless apologies into the hollow of his throat, Severus finally murmured, “You only love me when no one’s looking.”

Sirius didn’t answer.

Because it was true.

And he didn’t know how to stop.