At some other point Sirius might have laughed at his brother's outburst, it was very unlike him. But at the moment he had far too many thoughts swirling through his head as he tried to sort them out to find much humor in anything really.
He shook his head when Regulus went on. "We didn't exactly talk about it." He pointed out, they'd been far too quick to jump to assumptions and too much on edge and too ready to fight than use their words. And the words he had used weren't exactly explicit about what he had or hadn't done. But he hadn't felt like explaining it to Snape, not then, not like that, not after he'd jumped to the immediate wrong answer.
"Dumbledore didn't know, the whole point of what we did was so that everyone thought I was the Secret Keeper. That was the plan, that's what Dumbledore and everyone else knew. It wasn't until it came down to it that we changed things." Sirius didn't blame Dumbledore, or anyone else but Peter for what had happened. No one questioned him because it was what everyone knew to be true and Sirius didn't hold a grudge about that. It was a bad time, everyone was jumping at ghosts all the time, and two of the brightest gone. No one bothered asking questions, because they knew what had happened, there had been only one way that Lily and James could be found, and he was their secret keeper.
"I don't know." He admitted, he didn't know what he felt about all of this. "I'm not bleeding anymore." That was about as far as he'd gotten.