It will be only one of his many regrets, and yet it will be one he will think of more often than the rest. But Will does not know this now, standing here with Djaq and holding a simple wooden tag that means more than words, currently. And Allan will never know it.
They were friends, two boys who learned to be men together. From Allan, Will learned to laugh and to relax in the presence of friends. From Will, Allan learned to trust and the value of stopping to think. They balanced each other out, forming an odd but close pair. Even Robin saw it, and chose to partner them up more and more often.
But somewhere along the way, maybe as Will noticed Djaq more and more and Allan noticed them both, their friendship drifted apart. And then Allan was gone, and Will felt nothing except hot anger at his betrayal, and a little hurt - if he let himself think about it. But he tried to just forget, and move on. And eventually, the anger smoldered long enough that it ceased to be a burning fire, and the two of them shook hands when it mattered most. Allan took it as a sign of forgiveness, but to Will it was only because at that moment he somehow couldn't muster up enough anger to stop himself.
And later, Allan came back, but there was no time for conversations because Marian was in trouble and the Sheriff was going to kill the king and they had to get there and stop it because no one else would and it was all such a rush that Will never even thought about trying to repair their relationship.
And then they were there, and the whole dying in the desert and saving the king and watching Marian die never really seemed real to him. His body kept moving, and he spoke and responded at all the right times, but it all seemed like just a bad dream that he would eventually awake from. He was still half-dreaming when Djaq asked him to stay, and at that moment nothing mattered except being with her so he said yes. He didn't think about all the problems with that idea, like Luke in Scarborough and him being an Englishman and her being a Saracen and him not speaking a word of Arabic. And he certainly didn't think about the gang, or Allan.
The few days of recovery for Robin passed quickly, and then they were leaving and he had to tell Robin that he and Djaq were not coming. It was hard, to see the emptiness in Robin's eyes and have to add more bad news to it - but the emptiness meant that Robin didn't have it in him to care that they were staying, and the goodbye was quick.
And so the four remaining members of the gang left, with a pigeon from Djaq and encouragement from the King and nothing else. Later, Will remembered the sadness in Allan's eyes as he passed by to collect the bird from Djaq. Later, he remembered how quiet he was when he should have been making jokes. But then, nothing really seemed to matter that much except being with Djaq. And there didn't seem to be anything left between them to say goodbye to.
So he said goodbye to only Robin, with an apology for everything that no one really wanted to acknowledge, and let the others go with nothing from him. Djaq said goodbye to all of them. She was probably the only one who was currently able to comprehend what had happened on those hot sands and what it would mean for the future; and so she was the only one who managed to produce the time to say goodbye.
In the coming weeks, as the fog of Marian lifted off him and he began to understand exactly what he had done by agreeing to stay here, he found himself regretting many things. But the one he dreamed of most often and ached to redo the most was saying goodbye to Allan. Over and over again he wondered how their friendship had disintegrated so far that he had found nothing to say as they prepared to part ways forever. He should have at least forgiven him, let him leave without the guilt of the past. He should have said how much he meant in the first weeks of camp, when he was the only bright spot on rainy days. He should have thanked him for all the camaraderie they had, even at the worst of times. And he should have apologized for hating him. Because even though betrayal is still the ultimate sin, none of it really matters now, when he is gone forever.
And no matter how many times he dreams of it or wishes for it to happen, Will cannot turn back the clock. Time comes and goes, and leaves the unprepared in its wake with only regrets. There are many things Will regrets, but this is the one that keeps him awake more nights than any other and haunts him more times in a day. He sees his old friend in so many things here, in so many places where he has no right to be showing up and grinning that cheeky smile. And he notices his absence with every awkward silence, ever look he gives that no one is there to receive, every time Djaq starts to say something and stops mid-sentence because there is no one there to appreciate it.
But this regret is not one that can be fixed, and so he learns to live with it, same as all the rest.
And Allan never even knows that Will would still call him friend, if given the chance. He never gets to know.