And because he'd been such a fool, he'd almost lost his soul. He blamed himself endlessly for the fact that Peter wasn't captured that night. He'd let himself get so caught up in the moment that he hadn't been prepared for the full moon that arose as he left the Shrieking Shack.
He'd gone from blind rage at the sight of Peter, to relief at having gained Remus's understanding and forgiveness, to euphoria at having told Harry the truth, to ecstasy at the thought of freedom, exoneration, and Harry living with him and being able to give him all the love he deserved, to panic at the sight of the full moon, to terror and grief as he was captured by the Dementors, to blank nothingness as he fell unconscious, unable to cope with all the memories they brought out.
And then, the next thing he'd known, he'd woken up in the Charms classroom, only to be confronted with the sight of Albus Dumbledore himself. The man had listened calmly, just like he was doing now, as a heartsore Sirius gave his explanation, twelve years overdue.
Yes, he'd failed before. He'd broken promises, neglected his duties, and in his estimation, was the worst godfather known to man. But as he thought of the young boy lying in a bed only a room away from him, he swore he'd do things right this time. He would make it up to his godson if it was the last thing he did. He knew Harry would never be the same after what he'd seen tonight; the haunted look in his beautiful emerald eyes would never escape Sirius's memory.
He couldn't even imagine the weight of guilt and grief the boy now carried. What was worse was the fact that Harry now carried the same guilt that Sirius had been weighed down with for twelve years: the belief that someone's death was directly because of them. Sirius would never let go of the fact that Peter had been Lily and James's Secret Keeper because he'd convinced them that he would be the best choice. From now until the day he died, Sirius would carry that burden.
And Harry was like an open book; it was obvious to Sirius that the boy blamed himself for the murder of Cedric Diggory. How would Sirius ever be able to convince him that the boy's death wasn't his fault in any shape or form?
And it was in that moment, right then and there, that Sirius vowed that he would see to it that Harry would not travel down the same road of guilt, self-loathing, and depression that he himself had travelled down. Because Harry Potter did absolutely nothing wrong during the events of tonight, and had, without a shadow of doubt, shown bravery many grown witches and wizards would not.
Dumbledore opened his mouth then, and Sirius was jolted back to the present: the two of them, sitting in this office, discussing the fact that Dumbledore wanted Sirius to be away from Harry, to start talking to the old crowd, to get the Order started again, now that Lord Voldemort, the most evil wizard to ever live, had returned. Of course, Sirius knew how gravely important this assignment was - but he still wouldn't budge. There were others, others who could do the job, and do it well. He had a guilt-ridden, grieving, traumatized godson to help, protect, and love.
"Sirius, you have never failed Harry," Dumbledore said gently. "And he is not alone, you know that. He has his friends, who will make sure that he is taken care of. And he understands that there are assignments that take precedence over anything else. Voldemort must be stopped, and we both know you can be the rallying point we need. You mustn't worry, Harry is a strong young man. He will come through this."
A look of rage crossed Sirius's face again, but with an effort of Herculen proportions, he controlled it. But when he spoke, his voice was firm and unyielding. "Harry may be yours and the wizarding' public's sainted "Boy Who Lived," he said harshly, "but he is also just a child. And he is strong, I don't doubt that. But even the strong can only take so much. What will you do, Dumbledore, when he falls apart? I am not, AM NOT, going to allow that to happen. And don't go preaching to me about how important the Order is, I know that Voldemort needs to be destroyed. But I won't let my godson be destroyed along with him. For the final time, my answer is no, Dumbledore. I'm staying with Harry."
And with that, Sirius Black walked out of the office, not looking back at the old man behind him. It was time for him to fulfill his promise. He was going to go to Harry's bedside, and he was going to sit with him all night as he slept. And when morning came and his green eyes opened, he would have someone there beside him, now and forever.