"Sabrina had to drag Ronnie with her so I wouldn't be alone with him and his two friends. Ronnie seems... a little on the homicidal side, but otherwise fine, I suppose." As long as he didn't try to kill Regulus, they were fine.
Regulus turned around and started to walk toward his room. He took his wand out and cast a privacy spell around them. "What's wrong?" He knew something was wrong, because Sirius wouldn't normally stop and chat, and he wouldn't want to get tea. "Are you all right?" As much as he disliked Sirius, he knew that he'd always love his brother. The two were very different emotions after all.
Explaining all of that would be hard, almost impossible, and to avoid the silence, he spoke of nonsense that would give Sirius the option to share what was bothering him or not. "Did you see? They want to have a fancy party to celebrate one year here? Wear fancy clothes, dance. That might be fun."