1 year after Arthur's death, Merlin cried. The wound was still fresh and he refused to believe it had been a year. He still heard Arthur's voice in his ear wherever he went, saw shadows of him everywhere.
15 years after Arthur's death, Merlin realised he wasn't aging the way the others were. Gwen had pointed it out actually, how his face was still soft and young like it was in Arthur's time, while hers was littered with smile lines and signs of a life well lived. He still found it difficult to look in the mirror without thinking he saw a blonde figure in his periphery.
30 years after Arthur's death, Camelot was thriving. Gwen was a good Queen, and with Merlin and the knights at her side, she ruled strongly and fairly. Magic was once again legal and on bright summer days you could hear the hum of it flooding the streets. Camelot had become a safe haven for druids and magic users, and Merlin hoped Arthur would be proud.
50 years after Arthur's death, Gwen died too. She had been ill for a while, a lingering winter cough that persisted. Most of the knights had gone too by then, most peacefully surrounded by those they loved. Not like Arthur.
51 years after Arthur's death, Merlin left Camelot. The citadel was too full of painful memories, of whispers of younger days. There weren't many people who remembered him now anyway, only a handful of aging knights from Arthur's time. He told himself he wouldn't be missed.
150 years after Arthur's death, Merlin heard the news that Camelot had fallen, overrun by Saxons. He tried to find room to care but loneliness, and time had numbed his emotions. He was already mourning so much. The grief would come back of course, when he was least expecting it.
200 years after Arthur's death, Merlin thought he saw Leon, out of the corner of his eye, at a market in some nameless town. Couldn't be, of course, Leon would have died years ago, back in the old days of Camelot. Must be his mind playing tricks.
300 years after Arthur's death, magic was starting to disappear. The druids were dying out, and with no one to teach the young the ways of the old religion, it began to fall into disuse. Tales of fae folk and sorcery, curses and changeling children began to fade into legend, superstition for the anxious mind. Only Merlin knew it was true once, that you used to be able to hear the hum of magic just walking through the city. He was once called the greatest sorcerer to walk the earth, a long time ago. Does that still ring true when he is the only one?
500 years after Arthurs death, and Merlin was sick of kings. None of them would ever match up to Arthur, with their endless wars, their inability to coexist, their thirst for power that could never be satisfied. He longed for the old days of camelot, days that were getting harder and harder to recall.
800 years after Arthur's death, Merlin was giving up hope. Many had written about the two of them now, about the knights and the quests they took, about Gwen, and the sword in the stone. They all said the same thing, Arthur would rise again one day, when he was needed most. Merlin thought that was bullshit. He needed Arthur now, and where was he? Magic was starting to be hunted again now, much harder than before. With the lack of actual magic users, anyone could fall under suspicion. Little did they know, it had all died out long ago. Merlin had watched it happen.
1000 years after Arthur's death, Merlin made a friend. Her name was Freya, the daughter of a catholic priest, fed up with the restraints of her life. She had shiny gold hair and bright eyes that reminded him of Arthur. She asked him to marry her and and he said no. They all die far too quickly.
1200 years after Arthur's death, Merlin realised what he should have known all along. He was in love with Arthur and always had been. God, how much time he had wasted.
1223 years after Arthur's death, Merlin stopped counting.