Sirius hadn't come to talk about why he was an idiot, for all his grandstanding and bravado, Sirius was fully self aware of all of his short-comings. "He's a lot." He said rather than anything else, Jamie had been nice and he'd been a font of future knowledge, but he'd been a lot, too much in some regards. Sirius liked him, but he didn't want to delve too deeply into the future that stretched out ahead of him, he might not even go back to it. Whether by his own choice or the hotel's whims. So hearing about it from Jamie or anyone else hadn't exactly been a priority before now. And he wasn't even sure he needed to know anything about it now either.
"I didn't come here to talk about Dumbledore, or what people should have done." He snapped, he didn't fully disagree with what Regulus was saying, he just didn't have it in him to go back and forth about it, about the Potters or his role in their death or anything else about it. "We can't change what happened, it doesn't matter what he did, he's not here, and frankly I don't care." He couldn't get into all of that, not with Regulus and certainly not now.
He sighed too, he was tired, and he felt hollow, like the blood he'd lost days before hadn't actually been replaced when he came back. He just felt empty inside. "Unstable sounds right." He admitted.