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Merlin was so old now. When he'd first taken up protecting Arthur, he'd never expected to make it to his thirtieth summer at the latest. Here he was, centuries old, and aching from it. He'd seen Camelot fall, and kingdoms rise and fall in its place.
Through it all, he'd had one constant. Leon.
Drinking from the cup of life hadn't just brought him back that one time, it had kept him alive for well, as far as they could tell, ever.
It was just the two of them, Merlin and Leon, watching the world become something they wouldn't have been able to comprehend back in Camelot.
Age had changed them, certainly. Some things were still the same though. Leon was still the knight from Camelot, and Merlin was still the sorcerer scared for his own safety.
At least in their perpetual existence they had each other, and they had certainly grown together in their immortality.
They were reliant on each other. The only other person they could truly share their tired soul with. Leon was the only person that would understand Merlin's very long life, and Merlin was the only one that would understand Leon's.
In truth, Merlin had always been drawn in by the knight, but their forced eternity together had brought them closer. They'd shared so much, it had only been natural for romance to bloom after so long together.