"Sod you, it's not as if I never tried, Reggie. You blew me off whenever I tried to talk to you, and I got brassed at you for being a little prat. Where you ended up wasn't my fault." Sirius sounded defensive. Largely because some part of him wondered if it WASN'T his fault. He'd given up on Reg, after all. He'd had his reasons, but he still had.
"I know what it is," Sirius answered. "I don't know why you think Harry should know." Not that he wasn't caught up to his eyebrows in this mess, but it still didn't make sense.