It started with Gwaine. Long before the whole knighting ceremony though, Arthur was sure of it. Seriously, what was with that touching in Jarl's dungeon? It was so much more than an innocent "Hey Merlin, how ya doing?" sort of thing. It was a full on stroke-his-shoulders, look-deep-into-his-eyes, let's-talk-like-we've-slept-together-and-silly-Arthur-knows-nothing-about-it kind of greeting. So not on. And Merlin, the harlot. He just stands there smiling like the bumbling idiot he is! Disgraceful!
And then there was Lancelot. Oh he might look like an honest, well-meaning, completely straight man. But really? He's as bad as the rest of them. He may have started with his eyes set on Gwen, but did it take much to make him back off of her? No it did not. There weren't even words spoken! And then he moves right on to Merlin, he does! It was quite obvious that he had his eyes on the boy. Not everyone was asleep that night. Arthur totally knew why they had slept so close together. Really Lancelot should be ashamed, cuddling up to his Merlin. And within ten feet of everyone too!
Elyan. Elyan's probably the best behaved of the bunch. He hides his Merlin fascination well. At least that Arthur can tell. So far Elyan's not made his move on the poor innocent country boy. But the stares. Arthur sees the stares. They linger a bit longer than Arthur would like. Two seconds too long to be exact. Maybe one of his super scary Prince Arthur Pendragon Glares™ will do the trick and deter Elyan from making moves on his Meriln. Yes. Yes it does. Ha.
Percival has only been around for a day or two and already he's sniffing around the servant like an over-eager puppy. It was flattering when he showed that same enthusiasm at getting to call Arthur by his name, but it's not so flattering when done around Merlin. And Merlin. Merlin is probably the only person in existence to match his excitability. Arthur's pretty sure he's seen Percival flash his biceps once or twice in Merlin's general direction. He has to clench his jaw very tightly, not to yell obscenities, like the fact that Merlin can stare at his muscles if he wants to, no need to drool so much over Percival's.
And then, after much glaring and much wallowing in self pity and much much much jealousy-induced mental raving, Merlin catches him alone at night. He just stares at Arthur a moment, trying to work out what to say. Then he smiles that adorable smile that transforms his face from slightly-handsome-if-you-like-that-sort-of-thing to the most angelic face ever. "Really Arthur. And you say I'm the idiot." Rolling his eyes—and oh my god, have you ever seen such a deep and perfect blue?—he leans ever so closely into Arthur's personal space and kisses him on the cheek.
Ok, so he might have a slight possessive streak when it comes to Merlin. But really, it's only because he was an only child. And Merlin is his servant; he might be the worst manservant to ever grace the halls of Camelot, but still. He's Arthur's. So back off pretty boys. So go swing your hair and flash your big muscles. Either way, Merlin is his.