A/N This was inspired from quotes from episode 2 of season 1, and takes place in an unspecified time in or after the last season. Oh, and: my god... I am so depressing.
Summary: Uther had once asked his son, "How can you trust a man who's lied to you?" You can't. Of course you can't... but it's not that simple.
Merlin knew that he could not protect his secrets forever. One day, all of the half-truths and outright lies he had told to keep his magic hidden would come crashing down around him. Merlin didn't know whether it would be because Arthur had fulfilled prophesy and united the lands of Albion, or because some mistake on Merlin's part would lead to his discovery. On his good days, he could hope ardently for the former; he could almost see a future in which magic was free, again, and the hate and pain could stop for all of them.
On his bad days, Merlin was sure that it would be the latter... after all, his luck could not last forever. There had been too many close calls and too many people held – unknowingly – all the pieces that made up the truth of him for no one to see through it, eventually. In the midst of a crisis or when someone came that close to finding out about his hidden life, Merlin's greatest fear was that he would be found out too early for anyone to trust him again.
On the worst days, in the dog watches of the nights when he could not hide from the whispers in his heart, Merlin knew it probably wouldn't matter which path took him to his revelation. Because no matter how his lies were revealed... the result would be the same, in the end.
He had known this for a long time, though he only thought of it when he was alone in the dark. Long ago, he and Arthur had had one of their first truly honest conversations, when Merlin had ousted Sir Valiant as an imposter with deadly intentions. Arthur had spoken to the court against Valiant, for all that Merlin had said, and he was disgraced for it. When Merlin could not provide reasons for his accusations, Arthur had dismissed him from his service. "I need a servant I can trust," he had said, angry and disappointed and more adult than Merlin had ever seen him.
Arthur could trust Merlin with his throne, with his kingdom, and with his life and they would be as safe in Merlin's hands as in his own. Because Merlin lived for Arthur. He had duties to Gaius, and love for the physician and for his mother, for Gwen and Gwaine – but they always took second place to his king. It was something Merlin didn't think on too often; like breathing, it came naturally.
Naturally only until one paid attention to it, and then the rhythm was thrown off.
Because though he lived to keep Arthur safe, and to guide him to his destiny, Merlin had been lying to Arthur since the day they had met. Never once, when it truly mattered, did Merlin tell his friend the truth. All the pieces that made up who Merlin really was were missing in Arthur's understanding of him. His king did not know about the isolation of growing up with a deadly secret, and the importance of Will as his one friend who knew who he was. He couldn't know what it had been like to lose Freya, to lay her to rest, alone. Or know that when Merlin had sat outside all night during Arthur's vigil for Uther, that he had done so knowing what it was like to have your father die in your arms. Arthur didn't know of all the dangers Merlin had faced, the fears he had overcome, the secrets and plots and manipulations he had uncovered... because Merlin had hidden them all away and had shown only one part of himself.
Merlin could be terrifyingly dark. He carried within himself a power that most couldn't begin to comprehend; with a thought he could beat five knights of Camelot, with a word he could down an army in dragon's flame. He had defeated sorcerers with centuries of power in their grasp, had broken spells that spanned kingdoms, had saved countless lives... and most of this done on reflex and instinct. With the time to research a spell... his power was limitless. And anything that was limitless was frightening.
Merlin could be unbelievably good. He willingly sacrificed himself for others and was fearless in the face of danger when it meant that he was doing something right. He honestly didn't see the differences in people, didn't understand why those people should suffer or thosepeople should go without because they were born a certain way, or believed a different thing... or practiced magic. He saw beyond the fears that held other people trapped by prejudice or tradition. He saw the good in everything because he was connected to everything; his magic touched it all.
The part of himself Merlin gave to Camelot was a pale shadow of what he was, whole. And though Arthur suspected there was more to his friend, it was still the only part Merlin had ever shown him.
Uther had once asked his son, "How can you trust a man who has lied to you?"
You can't. Of course you can't... but it's not that simple.
Everything Merlin did was in Arthur's interest. Everything he did was to keep Camelot and its king safe. All of his sacrifices, and all of his lies; all of his life for so many years had been with one goal in mind. And he knew, staring into the dark with only his fears for company, that his final sacrifice, his greatest one, would be his friendship with Arthur, at the end of it all.
The truth - though Arthur didn't know it yet - was that he could not trust Merlin.
Because, no matter why they had done it... how could you trust someone who had spent your entire friendship lying to you?
And how could you be friends with someone you had never known?
You couldn't. Arthur wouldn't. But he would be safe. And Albion would be whole. And though Merlin knew the day would come when he lost everything, he would rise with the dawn and he would keep his secret, no matter the lies it required.
And he would not realize, for another day, that there were two sides to the fickle nature of trust. Because it wasn't that Arthur was not able to accept all that Merlin hid within his lies.
It was that Merlin didn't trust him to.