It was the look on his face.
When Arthur was with her, Merlin's face was different. His eyes were empty. His smiles were forced. The laugh lines, the squinty giggles, the wrinkled forehead. Gone.
It hurt.
It hurt both of them.
Arthur knew he had to be with Gwen. It was his destiny. She was his destiny. Not Merlin. Not the one he loved. Not the one he wanted to spend every waking hour with. Not the one he wanted to breath in and breath out, to hold, to have. Not him. Her. He did love her. But it was different. She wasn't him.
She couldn't be him.
It wasn't right.
Arthur couldn't be with him.
However much he wanted to.
However much he wanted to have him be the one sharing his bed. However much he wanted to have him curled against his side at night, his cold toes pressed in Arthur's calves, his arms draped across Arthur's chest, his face buried in his shoulder, the smell of his hair filling his nostrils. However much he wanted to spend all night watching Merlin sleep, holding him close to his side, feeling their shared warmth. However much he wanted to open his eyes to Merlin's smiling face in the morning, to kiss the boy awake until they were both breathless under the sheets, to stay in bed until the sun had risen and they knew they had to peel back the covers and face the world, but it was okay, because they were facing it together.
However much he wanted to, he couldn't.
He couldn't because it was Merlin.
It was Merlin, his manservant. Merlin, the clotpole. Merlin, the one who mucked out his stables and did his washing. Merlin, who drew his bath and brought him breakfast. Merlin, the idiot, the prat, the dollop head. Merlin, the one he loved with all his heart, but could never be with, simply because he was Merlin.
Because those were the rules.
And the King must follow the rules.
No matter how much it hurts.
No matter how much it made him want to rip his heart out.
He could never be with Merlin.
No matter how much he knew that Merlin was the only one in the world he would ever really truly love.
