HE WAS A CHILD. THEY WERE ALL CHILDREN. The Potters were five years younger than I am now when they were murdered and they'd already been fighting the war for years!!!!! Come on, dude, you've got a lot of unrealistic expectations here. When I was 21, I was in no way, shape, or form a rational human being who knew how to make all the right decisions all the time, let alone in a situation where I'd likely have been at my absolute most emotionally distressed. Like, Sirius Black was utterly destroyed that night. He made mistakes, yes, but they make sense given what we can assume about where his head was at in those moments!!
You're wrong. Like, I can't even tell you how deeply offended I am that anyone would ever claim that Sirius Black didn't love that child with all of his heart. Was he a good parent type? No, not really. Chalk that up to the fact that a) he was young, b) spent most of his adulthood in prison, and c) did not have parental role models until late into his childhood. Some people just aren't kid people, in general. I love Dahlia more than life itself, but I'm at least 99% sure I never want to have my own child. That doesn't mean that Sirius didn't love that child the absolute best way he knew how. Sirius was flawed, absolutely. No one's perfect. But I am not even joking that I will literally fight you to defend that man's honor.