It takes longer for Merlin to become accustomed to Camelot than it does Arthur to become accustomed to Merlin. Arthur has had manservants - plenty, really, he’s a prince, isn’t he? - but he’s never had his own personal manservant. Before Merlin, they’d all been palace servants, simply given the task of assisting Arthur with his daily needs. Chosen simply because they fit the castle standards of servants.
But Merlin is his manservant in a new way altogether. Arthur gets to train him to suit what Arthur actually wants in a manservant. Not that Arthur knows what this is; no, it’s more guess and check. Merlin helps him figure it out, to a degree. Merlin is so truly himself, something Arthur has trained himself to believe is impossible for the Prince of Camelot, and so Arthur trains Merlin to think nothing of the Arthur alone who is nothing like the Prince of Camelot. Merlin doesn’t know to expect differently. It’s a relief.
Slowly, Arthur gives ground. He trains Merlin to be more a friend than a manservant. He lets slip, little by little, the parts of him that demand respect, that set him apart from other men. It doesn’t take much; Merlin had never really kept that distance particularly well, though he had seemed to try.
After that, Arthur just keeps giving ground. He trains Merlin to be a partner - albeit one who does all of Arthur’s chores - so that Arthur is never without that option to speak, or think, or do, not as the Prince of Camelot, but as Arthur, a young man still learning reason, right, and wrong.
A partner, Arthur realizes, is what he’s wanted all along. Perhaps his manservant wasn’t meant to fulfill this role, and he’ll train one differently in the future, though Arthur can no longer imagine anyone else in this role. Merlin is an excellent partner. He takes Arthur’s jibes and reprimands and learns to give as good as he gets.
He also goes anywhere Arthur asks him, takes any risk, buoys Arthur’s spirit, and sometimes surprises Arthur with his ability to say exactly the right words. Arthur expects Merlin to be by his side, to be on his side, and he is almost never disappointed.
When Merlin isn’t with him, can’t be with him, Arthur feels the empty space like a wound. He finds himself less relaxed, with his muscles tight, and his mind not quite so quick to find the right solution. Arthur knows that this is a weakness he’s allowed himself. He knows that the Prince of Camelot ought not to have any weaknesses.
He also knows that if Merlin has taught him anything, it’s that Arthur and the Prince of Camelot aren’t meant to be separate people. That truth, fundamentally against everything Arthur has ever been led to believe, has done more than just help Arthur become more himself, more of the time. It has also made his ruling more fair and his judgment more wise. Since Arthur met Merlin, he has learned that the commoners have sense that the royalty does not. He has learned that there are as many shades of grey as there are people in his land. He has learned that sometimes what is right, is not always logical or lawful.
He has learned that what Arthur has learned, the Prince of Camelot, too, should learn.
Merlin is everything Arthur cannot be, but somehow, that’s fine. As long as they stay together, they are everything Camelot needs them to be.
Arthur has no intention for them to ever be parted.