Sirius had siriusly thought that perhaps Harry would kill him, and somehow his tired mind accepted the possibility as fitting, for even if he hadn't done so on purpose, his actions had resulted in James' and Lily's deaths. Remus' sudden entrance put a stop to that however, and his breath caught in his throat for a moment, before he found himself laughing at Remus' comment about the madness within. How familiar this scene was, and yet so strange.
And did Remus hate him too, blame him for what happened? That would explain not coming to see him once in twelve years.
"You should know all about the madness within, Remus," he said cautiously, as if testing the waters, to see what they might hold.