"Don't get caught."
The only words he'd heard from the Prince when he'd woken up to find Arthur looming over him where he'd been sleeping slumped over Gaius' workbench, his head pillowed on his magic book and Arthur's breeches mending themselves on the table in front of him. Then Arthur had turned and strode from the room, leaving Merlin with his heart pounding in his chest and a million explanations balanced on the tip of his tongue.
"There is no guarantee that I can protect you if any of the knights accuse you. So if you do anything, make sure that they don't see."
The first not related to chores that Arthur had spoken to him in the month since he'd learned Merlin's secret, his voice low but intense and his grip on Merlin's arm desperate with his anxiety. They had been just about out with a group of knights behind them to confront the latest to Camelot's safety, another deadly creature that could only be destroyed by magic and they hadn't been much but Merlin had clung to those words like a lifeline.
"Try not to get yourself killed."
The last words Arthur had said to him before he'd charged head first into danger, as he always did. If Merlin had had the time, he would have considered the grim irony of those words. But there hadn't been time. They'd been separated from the group and Arthur had been bleeding out all over his hands, and there just hadn't been time. It was Arthur who had been dying, right there in Merlin's arms, and Merlin was never going to get the chance to apologize for lying for all those years. He wasn't going to get the chance to tell Arthur that he'd never wanted to lie to him but he'd just been scared. And then Arthur had started coughing, awful wet coughs that wracked his entire body, and Merlin's magic had just ripped through him in a great burst, cloaking the Prince in shimmering gold before dissipating across the clearing. As he watched the pain wash from Arthur's sleeping face, not even the harsh "You will release him, sorcerer" could make Merlin regret what he'd done.
"You have bewitched my son and you will burn."
As the king, the swiftness with which Uther could end a life was something like its own kind of magic and if Merlin were a different man, hearing Uther Pendragon sentence him to death might have made him break down and tremble. But he wasn't a different man. He was Merlin. And that meant he was Arthur's. And Arthur's words, shouted across the Great Hall as he struggled in the grips of two guards, had a magic of their own. So Merlin just sat back in his cell and watched the sun rise.
"I will come for you. I won't let him take you. Never you."