It was some time after Sirius's death that Remus began to think about Azkaban.
He had wondered about it, during those twelve years that followed James and Lily's death, after the shock had ebbed and reality sunk in. With his knowledge of dementors, Remus had predicted that after one year, Sirius would no longer truly sleep, would not remember what sleep really felt like, so horrible and unbearable his nightmares would become. Sirius would be in constant pain, throat raw from screaming.
This thought did not make Remus feel better, and that made him feel even worse.
Three years later, Remus thought numbly, Sirius would probably have fallen completely silent except for in his dreams. He gave Sirius three years because somehow he couldn't imagine Sirius giving up so easily, for if nothing else Sirius was one of the most brilliant and determined students Hogwarts had ever seen.
Remus realized that this was how he still thought of Sirius, in the quiet, sheltered corner of his heart, still felt the laughter and the touches of him on his skin, not-quite ghost fingers running down his spine. They couldn't be ghost fingers, not with Sirius so alive and brimming inside him.
Much later—seven years later-- when Remus had just began to think that maybe, possibly he'd put most of it behind him—not forgotten, but present only in the quietest murmurings of his thoughts—the night of Halloween 1988 he woke up screaming, and crying Sirius' name, and wishing he could sink into the madness that Sirius must doubtlessly have fallen into by then.
The moment passed, and Remus grieved for James and Lily and Peter. A part of him cried out for Sirius, but then he realized he could not grieve for what he'd never had.
His chest twisted, and tears fell anyway.
The Halloween of 1993 was different because Sirius was possibly mad, but no longer silent, his presence impossibly loud and inside Hogwarts castle. Remus didn't know what to think or do, how to handle the escaped prisoner—for that is what he was, escaped from the prison Remus had locked him inside long ago—and memories came unbidden to him, things he had suppressed over the years. Sirius grinning at him over dinner, arm brushing his under the table. His leg twining with his under their work desks during potions (Remus never had a chance of passing that OWL). Their shared heat in Gryffindor tower—
It's the castle that's doing it, Remus had thought, and wondered how everything was going to end where it had all started.
Then, Sirius was innocent, and it wasn't the end after all.
Up until the Department of Mysteries, Remus Lupin's life had taken an unexpected turn, and he rediscovered some of the happiness that he had been denying himself for years. Even working for the Order was better, because he was working for a cause, not just to scrape by, and Sirius was with him, not just in echoes, but in his loud, reverberating voice. And that was more than enough, more than Remus had ever imagined he could have again.
After the Department of Mysteries, Remus realized they had both been living on borrowed time.
When Sirius was lost to him before, he thought always of Hogwarts, how things had been, until he stopped himself and let the present reclaim him, distract him from the uneven beating of his heart.
Now that Sirius was lost to him again—forever, this time, Remus knew—he thinks about Azkaban instead.
Remus now knows why Sirius didn't go mad in Azkaban. Sirius had said it was because he knew he was innocent, but that was only partly true.
The thought probably had helped him keep his sanity, but Remus realizes that even so, without his true memories, Sirius still would have gone insane.
It is the devastating power of the dementors to make a man relive the worst moments of his life, to make him wallow in the worst emotions ever experienced.
For Sirius that would have been guilt.
Guilt because he thought it was his fault that James and Lily died, guilt that he'd ever doubted his lover, guilt that he hadn't seen it all—and from that guilt he would remember what he had lost, pushing his innocence into the clinical part of his mind where it wouldn't get in the way of his tortured soul.
Looking back on Azkaban, it was Sirius' guilt that had saved him, and his love. That was why Azkaban had worked so horrifyingly well on him, and why it could never work terribly enough for the man currently at the end of Remus's wand.
Peter doesn't deserve the escape of madness, the escape Sirius never had.
Remus looks at the man who for twelve years had been his real curse—worse still because he hadn't known it—and found that he felt numb.
Yours, whispers Sirius, spoken long ago but never forgotten, the hushed word like ghostly breaths against his ear.
He thought it had been the end after the Halloween of 1981, and he thought it had been the end after Sirius's death. He realizes that it hasn't come, not yet.
His wand arm steady, Remus opens his mouth and begins.