It's not. You can't undo what you did, but you have to do better from now on.

[They're supposed to work together and trust each other. And that means everyone. So he feels like he has to try, even if he's running the risk of pissing Chuuya off.]

And I have to do better, too. I want to say you're wrong, that when it comes down to it we wouldn't all just protect the people who mean most to us. . . But I can't pretend that I didn't fight harder for Lio than I fought for Dazai! And that wasn't right of me, either!