there is a clear distinction between gof sirius and ootp sirius so let’s talk about it because it’s all i’ve thought about for days.
in gof, sirius lives in a fucking cave eating rats in order to be near harry during the triwizard tournament. this is a decision that puts sirius in danger — being so close to hogwarts with ministry officials prowling around could easily land him back in azkaban. but here’s the thing: sirius doesn’t choose to live in hogsmeade for a laugh, or for his own personal gratification. he did it to protect harry — in the cave scene, when the trio ask what he’s doing, the first thing he says is “fulfilling my duty as godfather.”
and he is. because throughout gof, sirius gives advice, guidance, and comfort to harry. he tells him not to take unnecessary risks, to stay safe, to focus on getting through the tournament alive. sirius chastises harry after he finds out that he went into the forest with krum, he offers sympathy when harry talks about the fight he has with ron, and also, he lived in a cave and survived on rats just to be close in case harry ran into danger.
consistently throughout gof, sirius is a comforting presence to harry. he is intelligent, protective, and even paternal. this is sirius black at his best.
and sirius black at his best stands in stark contrast to the man we see in ootp: angry, mercurial, moody. reckless. he constantly makes bad, impulsive decisions: seeing the kids off at king’s cross, popping into the gryffindor fire, picking fights with snape. in ootp, sirius causes harry more worry than he assuages — directly conflicting with his goal of fulfilling his duty. not to mention, his treatment of harry, which is in direct opposition to what he displayed in gof: now, he encourages harry, compares him to james, even guilts him — “you’re less like your father than i thought.” that’s a shitty, low thing to say to the boy you’ve sworn to protect.
and all of this is leading up to the crux of the matter: sirius’s obvious illness. he’s depressed, he shows signs of bipolar disorder, he has tendencies toward alcoholism. he’s likely dealing with some form of PTSD after twelve years in azkaban. these things are true of sirius no matter where he is, but in gof, he’s in a healthier state — ironically, given his living conditions.
the trigger for sirius’s behavior in ootp is grimmauld place. it’s imprisonment, it’s being locked up in a house that he loathed, one that he was almost definitely emotionally abused in. it’s being kept from having an active role in the order, it’s being goaded by snape, it’s being stuck and unable to help, all in a place that represents everything he spent his teenage years trying to escape.
hermione consistently points to sirius’s instability, says that she thinks he’s being unwise, and when harry takes it as an insult on his mental state — it isn’t an insult, it’s a correct observation — hermione says that he’s been lonely for a very long time. and she’s right. in ootp, we see the effects of all of this on sirius, and they’re invariably negative in the extreme.
it’s heartbreaking to see the contrast here, because in one book we see the best of sirius: loyal, selfless, protective, and loving. immediately following, we see the worst.
but even at his worst, even amid his own battles with illness coupled with the fucking infuriating things about sirius black, he protects harry. he goes to the ministry to fight because harry is in danger, and he dies protecting harry.
sirius was fucked up but even at his worst, he still fought for harry in the end because there was no way in hell the person he loves more than anything else could be in danger without him there to protect him. he lost his duel with bellatrix because he underestimated her, because he’s prone to losing himself in the thrill of the fight, because he couldn’t resist the temptation to goad someone he loathed.
but he went into the ministry that night to protect harry. he would have done it for james, sirius, remus, peter, or lily at twenty; he would have done it healthy in gof; and he did it as sick as he was in ootp.
in spite of everything that happened to him — and everything intrinsic to him, all the cruelty and grudges he clings to by nature — sirius is a good person.
because there is nothing sirius black would not sacrifice for a person he loves.