"I know your dirty little secret," Severus hisses, without looking up. Just like him, Remus thinks, freezing, to inadvertently say something so loaded, without thought or intent or even pausing from writing out his ingredients list.
"You don't know anything," Remus replies. He says this so quietly, so unsurely, that he knows Severus must suspect something: if not before, certainly now. Remus can taste his own fear in the back of his throat, even though he tells himself, he doesn't know anything, he can't, there's no way, it's secret. And yet somehow, he doesn't believe himself the way he should. "Just leave me alone," he repeats.
Severus does pause this time, setting his quill down on the desk carefully. He turns towards Remus slightly, and there's a look about him that Remus doesn't trust; a look in his eyes that wasn't there yesterday, a look that says, I know. And Remus has to check himself, to hold in the panic, to stay calm, because maybe, just maybe, he does know. He inhales sharply to say something, but Severus gets there first.
"It's okay," he says, softly, trailing his fingers down Remus' forearm, where Remus has pushed back the sleeves of his robe. He flinches. "Don't worry," Severus continues, and there's his breath on Remus' earlobe, again, "I won't tell anyone. It'll just be between you--" he pauses, and tilts his head so Remus can't help but look at him from the corner of his eye, "--and me."
Which, Remus thinks, is just what he wants.