Arthur is worried about Merlin.
He's talked to Gaius, but the physician says that Merlin is not sick. He is not insane, and he is not under the influence of sorcery. Nobody else seems to really notice. Gwaine says Merlin seems normal enough, and Percival agrees. Leon suggests that maybe Arthur is just being overprotective. Mordred says that Merlin has always carried a burden on his shoulders, but he doesn't think it's gotten any worse as of late.
Gwen says that Merlin is just worried about Arthur.
But 'worried' doesn't cover what Merlin is. This is deeper than that. It's like there is a disease eating away at Merlin's insides, and Arthur is helpless to stop it.
And then Mordred betrays them.
Arthur knows that it is his fault, no matter what Merlin says. The girl was a fanatic, tried and hanged for her crime of murder. Magic doesn't even come into it. But Mordred is young, no more than sixteen, and he is in love in that stupid, passionate, all-consuming way that teenagers have. Arthur can sympathize, can picture all too well how hard and desperately he'd have fallen for Merlin if his husband had waltzed into his life when he was sixteen instead of twenty.
Well, he fell hard and desperately anyway, but that's not the point. It was a different love, anyway, more tempered, more durable.
But Mordred cannot see that. He can only see his current heartbreak, and his blood runs hot.
Arthur should have reached him. He should have explained himself better. He should have done… something.
When Arthur comes to bed that night, all it takes is pulling back the covers for Merlin to jump him. He clings to Arthur, holding onto him, his entire body trembling.
"What's wrong?" Arthur asks. He settles them down on the bed, gives Merlin's shaking body a solid form to lie on. If he didn't know any better he'd say Merlin as having some kind of seizure.
"You have to stop going out to battle," Merlin whispers. His fingers trace the lines of Arthur's face, his eyes darting wildly about, taking in Arthur like it's the last time he'll ever see him. "You need to stay here, where it's safe."
"Merlin, you know I can't just abandon my men and expect them to fight all my battles for me. This is between me and Morgana. It's important that I ride out with my knights."
Merlin shakes his head, makes a wounded noise like an animal with its leg caught in a steel trap. "No."
"I'll come back," Arthur promises. He smoothes his hands over Merlin's skin. "I always come back."
"No." Merlin's voice is barely audible, hoarse and insubstantial. Arthur suddenly realizes that Merlin has been crying. He wonders for how long. "You can't promise that, Arthur."
"Yes, I can."
"So you know what the future holds?" Merlin's voice holds humor, but it is bitter and black. "You can tell me what will happen next?"
"No," Arthur admits. "Do you?"
Merlin doesn't answer, simply draws Arthur to him.
Later that night Arthur pulls Merlin's back to his chest, curling around him, trying to shelter him from whatever nightmares Merlin seems to see. Merlin presses Arthur's hand, his left hand, to his lips, keeps it there, whispers don't leave me, don't leave me, please don't leave me over and over again into the skin and the silver and gold ring wrapped around his ring finger, the words still illegible in their ancient script but their meaning burned into Arthur's soul.
Arthur holds him, holds him so tightly he fears bruising in the morning, but he doesn't lessen his grip. He isn't worried about Merlin now. He is outright scared for him. He is scared that he is losing Merlin, not to Morgana or disease or an accident, but to Merlin's own treacherous mind.
He fears that Merlin is breaking down.