The healers say friends and familiar faces would be good for him, people who can tell him about happy memories they share or correct the bad ones that the dementors have twisted; but the only one who can do that is currently in Azkaban for having helped kill the other two, and if Sirius ever sees him again he will commit the murder he had been sent to Azkaban for. And Remus... well, after a while, Sirius accepts that Remus is—gone, or will never come, and Sirius isn’t sure which one is more painful to him.