A little empty, on the inside. Like, a little numb? Maybe it was shock, or fear or something in between that had him out of sorts. Because James was gone and he'd only come back now and if Remus was right (and he was, Sirius knew he was) then James was either going back to die or he was lost behind some door and neither seemed ideal in any measure. It was terrible. It really, really was. The optimist in him wanted to think that maybe this had been lucky - that James had been here long enough for them to discover truths about themselves, each other. And for them to have seen James one last time, to have hugged him and talked with him and that was more than they thought they'd get.
Maybe that was the same for his brother too, although they hadn't really talked beyond that first day. Sirius didn't know, and his considerations on that were complicated but leaning toward nonexistent. Not for nothing maybe, but he didn't have it in him to have this many things going on in his head at once.
Probably it didn't help that he currently had all of the blood in his body rushing toward his head, either. It made things seem loud, even though it was quiet, but it was still probably his favorite couch position. Besides being strung all over Remus, obviously. "It would help more," Sirius said (upside down), "If you fed it to me."