Sirius wasn't going to apologize for forsaking their parents, neither one of them deserved even a second more of his time or thought. Regulus though. It was complicated at best, and impossible at worst and the more they talked the less Sirius wanted to do any of it.
"Before you go," Sirius began, because he was feeling more and more certain that they would just go on avoiding one another because they couldn't keep doing this. He didn't have the patience for it, or the heart to keep on fighting with his brother. "Whenever you've decided I've changed my mind come and find me again, we can try having another conversation." He told him. "You obviously know what I feel better than I do, so just let me know and maybe we'll try again. If I'm still here."