Sirius was still frowning as Regulus snapped at him, knowing all-too-well just how much his brother had warned him about Potter and his band of bloody misfits, but he hadn't listened, had he? And look where it'd gotten him. "That - yes, that is my fault. Entirely. The blame lies with me, and with the terrifically stupid things I did when i was young. But you must believe that they did something to me - I know not what it was, but it was something. There's a difference, between youthful stupidity and adult transgressions, and I know, had it not been for them, that it would never have taken me this long to come back. To fix things."
He sighed when Regulus brought up their father, once again feeling a jolt of unfamiliar guilt. "Again, I can hardly make apologies or excuses for that, but it wasn't me. Not the real me. I never would've behaved that way, had it not been for them and their influence."