Regulus catches enough of those emotions to piece together various aspects of the problem. He feels hollow, and cold, and bitter, and guilty. The step back means something, and there's a sharp, closed-off hurt that flickers across his face before he can shutter it away.

Before he can shut down his emotions before he starts to feel even more ill, seeing Sirius do the exact same thing he is. They're too alike in that way. Then Sirius is talking and smiling and--

Regulus takes a breath, shrugs noncommittally. "A while," he says, softly. "Not--not a very long time. I'm sorry for not saying anything, I just..." Another breath, this one almost shaking. "He's been helping me. I don't want to be like that and I can't..."

Do it alone, he doesn't say. Because that's cruel.