Once they start having sex, it becomes extremely difficult to focus properly on their schoolwork.
“Can I borrow your silver knife, Moony?”
Remus makes the mistake of looking up from his uncharacteristically not terrible attempt at a Calming Draught. Sirius is smiling politely, the first three buttons of his shirt undone and his tie hanging so low that it would be less conspicuous if he wasn't wearing one at all. He winks at Remus.
Remus turns away immediately.
Think of the Draught, he tells himself, sternly, gripping the tabletop with such force that his knuckles turn white. You're almost done brewing it, and Merlin knows you could use a decent Potions grade. It's going to be lunch time after we're done here, and if you just wait...
His hand shoots up almost against his own will.
“Professor? May I please be excused?”
“Mister Lupin? Are you unwell?”
At any other time, Remus would find Slughorn’s faintly alarmed tone pretty hilarious – the man is scared stiff of the idea of lycanthropy, to the point that even after five years he seems to always be bracing himself for an impromptu mid-morning transformation on Remus' part – even a sneeze is enough to make him reach for his wand. James once suggested that Remus go to his office after hours – complaining of an ingrown toenail, or an itchy nostril, or whatever – and see how long it takes for Slughorn to lose his nerve completely, Stun him in preventative self-defense and flee the school for good.
“Yes, Sir. I'm feeling a bit nauseous, I reckon I'd better head for the infirmary.”
“Certainly, m'boy, certainly. And hurry up, I might add.”
“I'll go with him.”
“Yes, of course, Mister Black, thank you... splendid. Well, off you go, then, boys.”
“You have to stop doing that.”
“Stop doing what, exactly?”
“You know perfectly well what I'm talking about, Sirius,” hisses Remus, shoving Sirius through a tapestry and into a nice deserted corridor. “With your shirt all unbuttoned like that and your winking at me over your cauldron.”
“I've always worn my shirts like this!”
“Yeah, but that was before I knew about the way you moan if I kiss you on your stupid chest,” says Remus, doing just that. Sirius makes a noise that makes Remus' cock twitch in his pants. “How am I supposed to focus on the process of adding Moonstone dust to my potion when you stand there and make it perfectly clear that we could be off snogging instead, huh? And don't get me started about the way you suck on your quill.”
“Moony, it's honestly not my fault if your interest is so easily, er, aroused,” he says, grabbing Remus' erection through his trousers. Remus moans. Sirius grins. “OK, I'm lying, sometimes I do it on purpose – if only because watching you try and fail to act all oblivious is almost as much fun as actually–”
Sirius trails off, his grin faltering, and Remus becomes suddenly aware of a shadow gliding ominously in the very corner of his vision. He swallows.
“You saw that too, right?”
“It was just the Bloody Baron, nothing to worry about,” he says, but he makes no further attempts at groping Remus. “Say, shall we go down to lunch? I'm starving.”
A few days later, they're on the spiral staircase that leads to the Astronomy tower – snogging – when suddenly the Grey Lady glides by, giving them a supercilious look as they are forced to separate and stand dangerously close to the banister in order to let her pass.
“What do ghosts care about what we do with our time?” mutters Sirius, once she is safely out of hearshot. “There was no need to give us that kind of look. I bet she's jealous.”
“I doubt she is, Sirius,” says Remus, with a pang of guilt. “They're probably disapproving of the fact that we're out of bounds. She knows there's really no reason for us to be up here during the day, let alone doing what we were doing.”
“Speaking of which,” says Sirius, with a smirk, and he gets back to it.
“Sirius, I have to go, it's our turn to patrol the hallways tonight – if I'm late again, Evans is going to jinx me into a jelly.”
“Say, how about we give James some Polyjuice Potion and turn him into you? That way he can go spend the evening prowling the hallways and being all sycophantic with Evans, and you can stay here and suck me off.” he says, wriggling his eyebrows.
“I don't think we have any more Polyjuice– ” starts Remus, and then he catches himself. “I'm a prefect, Sirius, I can't just give up my duties completely to stay in bed with you all day – tempting at that sounds – wait, are those biscuits?”
“Your favourite kind,” confirms Sirius, tilting the tin in Remus' direction. “Chocolate biscuits. Fresh from the kitchens – I know how much you enjoy them, so I had the house-elves bake them specially for you.”
Remus closes his eyes for a second.
“You know – come to think of it – I reckon we do have a small flask of Polyjuice potion left.”