It wasn't a matter of it being James or not James in front of him asking about Regulus; it was more a matter of it being a question about Regulus. "I didn't really miss him while he was gone, and he hasn't changed any, so it's really not much of a matter to need to talk about at all." Sirius fingered the shot glass, his thumb along the rim for a moment, and then tossed it back as well.
It wasn't one hundred percent true. He had missed his brother, but he had missed the brother he had growing up, not the one that he was splintered from based on the completely opposite ways their lives went.