What Merlin loves, loves, is to be bent over Arthur's table, fingernails scratching grooves into the smooth wood and the edge biting against his hips every time Arthur slams into him. And Arthur is slamming, a hand hard and heavy on Merlin's shoulder and the other o his waist, and even if Merlin wanted to get up-to shift position or stop—he couldn't, has to take it, whatever Arthur wants, whatever Arthur deigns to give him.
Arthur is hot at Merlin's back, breath scratching out of his throat but other than that so so quiet, and Merlin's the one who's gasping and mewling and begging, and Merlin could hate him for it—for laying Merlin wide open like this, making it obvious how desperate he is to have Arthur's cock splitting him apart, except for how much he loves it.
And Arthur's huge in Merlin's ass, fucking him so hard Merlin can feel it in the back of his throat—he could gag on it if Arthur just pressed in a little harder—and at that thought Merlin's mouth waters desperately, too greedy, always too greedy for every piece of Arthur all at once.
Arthur's a bastard, too, because he's deliberately missing Merlin's prostate except when he hits it dead on (and Merlin knows it's never an accident—Arthur knows just what he's doing, because if Merlin could twist he knows he'd see a smug look in Arthur's eyes), sporadic and not enough, but Merlin knows better than to reach for his cock (bad things happen when he takes liberties—things like Arthur finishing himself off and never once touching Merlin, and sending him back to Gaius still panting for it) and so he whimpers, "Arthur, please?"
Arthur bites the back of Merlin's neck and Merlin shouts as Arthur cants his hips and fucks Merlin into coming too hard too fast, on his prostate with every single stroke, screaming his throat raw and clenching down on the cock that's still brutally fucking into him, pressing back into Arthur's body.
And Merlin's knees are buckling but he's stuck between the table and Arthur, who finally, finally comes, hot and pulsing inside Merlin, and when he pulls out—still able to walk, the bastard—Merlin can feel Arthur's come dripping down his ass and his thighs, and he collapses against the floor, propped against Arthur's leg. From there, it's easy to turn his head and clean Arthur's cock with his tongue.
Arthur's hand settles on his head, fisting almost gently in his hair as Merlin laps at the tip and sucks Arthur's spent cock into his mouth.
"So perfect," Arthur murmurs, and Merlin smiles up at him, and if they're very suddenly in the bed, well. Surely it's just a trick of their sex-addled minds.