Arthur's a prat. A large, spoiled, smug, arrogant, pain in the ass, and yet.....And yet the feeling of said prat's hair falling through his fingers, his name moaned out, uttered with the equivalence of a prayer, that feeling has knocked out any sense he thought he might have had. There's the small, red marks hidden just out of sigh, covered by clothes during the day and remade, once again imprinted on skin as the night grows older.
He knows Gaius knows. That he's noticed his apprentice no longer showing up at the end of the day. That he only shows up in the morning, eyes dark with circles and hair rumpled from being pulled at all night long. There's the mark that Arthur couldn't resist making, right there on his neck. The one that makes him glad he likes his scarf. So yes, Gaius knows. But he knows better and keeps his mouth shut when he's making breakfast.
They fumble in the corridors, hands searching, scratching, marking skin. Uther's out and for once didn't take Arthur with him, and they're taking advantage of it. And each other.
Finally they make it to Arthur's room and he's on his stomach and so goddamned hard and words telling Arthur to hurry up, it feels so - oh sweet mother he hit that spot - good and he's sweaty and they're sticking together, bodies molded and Arthur (finally) comes and rolls off and this is his favourite part.
The part where Arthur strokes his back and he pushes that blonde, sweaty hair out of his eyes and they just look at each other before drifting off, still holding each other.
When he stops to think about it, he grins when he realizes that this secret is one that he really doesn't mind keeping. The thought is quickly chased away with a growl from Arthur and his wet mouth latching onto his neck. No, he doesn't mind at all.