Sirius Black survived the war and ran away with Remus to Spain and their lovely godson visits them every week. I don't know what book you guys were reading. They are happily married and living in a lovely little house together and it's always warm and happy and nothing like 12 Grimmauld Place.
Regulus at Grimmauld Place
-taken by Sirius, summer 1976
The last time he did something “muggle-ish” with his brother (though it was very funny)
Sirius Black who gets angry when he’s in 12 Grimmauld Place.
He’s just gotten out of Azkaban, just found a place he can rest after being on the run, so no one blames him when he’s a little bit fidgety and strange.
It’s incredibly odd when he flat-out refuses to sleep in his childhood bedroom, but everyone has at least an inkling that his childhood may not have been perfect, so they go with it with little argument. That doesn’t stop the confusion, though.
“I’d kill to have a night in my childhood bedroom, especially if my parents never changed it!” “It would be like being a kid again; no responsibilities, just time to relax!” “It’d be like going right back to your younger years, who doesn’t want that?”
Sirius leaves when they talk about it. They get the hint.
Then he starts to get angry. He starts to change. He starts becoming quiet and abrasive.
At first, it’s little things. He lets out an incredibly aggravated sound when he tears his breath while buttering it. He snaps at Kreacher when the elf mutters under his breath. He runs his fingers through his hair hard enough to pull some out. He eats less. He drinks two glasses of wine instead of one.
Then it gets less small. The people in the room right under his are woken up in the early hours of the morning when he punches a hole in his wall. He genuinely pulls his wand on anyone that touches him without sufficient notice. He smashes his fist into Snape’s face when Snape makes a comment about how spoiled he must’ve been as a kid. He stops eating entirely. He’s drunk more often than he isn’t. He’s not sleeping. He starts wearing clothes that cover every inch of skin on his body. He stabs a hole through the canvas of Walburga Black’s portrait when she huffs at the colour he’s wearing.
People start getting upset with him. He’s getting reckless, he’s getting violent, his mood changes at the flip of a dime, his temper is shorter than it’s ever been.
It reaches a boiling point when Sirius snaps at Harry.
Harry had just been trying to ask if he was okay, because even a teenager could see that something isn’t right. Sirius had reassured him. Harry hadn’t been convinced and had gone to hug his godfather from behind. Sirius had flinched away so violently that Harry had nearly collapsed, and then he’d yelled at the kid never to do that again.
Harry had run off. Sirius had retreated to Walburga’s— his— room. His first move is getting drunk off his ass, then taking off his shirt to look at the damage plastering his body. He tried to cover it all with tattoos, once upon a time, but it never worked. That was after he, in his Hogwarts years, had taken a blade and a blasting spell to his skin to cover up the damage that way. That didn’t work, either. Nothing worked. And being in that house just seemed to be ripping those old wounds open.
Sirius had to put wards for himself and only himself on the windows and balconies of the upper floors, that way wouldn’t be too tempted to see if he could fly without magic. Sirius had to move all the dangerous potions to a locked box, which he gave Remus the combinations for and then promptly obliviated the numbers out of his own head. Sirius had to lock himself out of the kitchen so he wouldn’t be able to get his hands on a knife. Sirius had to give Remus his wand so he wouldn’t do anything stupid to himself or anyone else after he pulled it on Minerva. Sirius had to put up barriers and take precautions because he knew what the house would do to him.
12 Grimmauld Place killed Sirius. It killed him every time he walked around a corner and saw blood and tears and bright red light from the tip of a wand in his mind’s eye. It killed him every time Kreacher glared at him and tried to slip something into his food, which he had to throw out before he ate it knowing it would hurt him. It killed him every time he walked by Walburga’s portrait and she grumbled or muttered or shrieked at him, just like she did when she was alive. It killed him every time he ran his fingers over the keys of the grand piano, found comfort in music, only to remember shattered fingers for playing the wrong note. It killed him every time he looked at the permanently locked door with the initials on it and thought of his baby brother, only little, coming to him for nightmares or because Orion and Walburga had forgotten to feed him.
Sirius Black wasn’t angry. He was scared. But no one could see it, because he’s become a master at hiding his emotions.
That’s why he was so excited when he heard that Harry needed help in the Ministry. It meant he could leave his own personal hell.