For a long time Regulus's friends don't like Sirius.
He's loud, reckless, and arrogant. He acts first and thinks later, following his heart with little care for the blood it may draw. They're resentful when he runs away and angrier when he tries to reconcile his and Regulus's relationship. And even when Regulus begins to forgive him, they refuse to.
That is until they realize Sirius has an endless collection of embarrassing stories from Regulus's childhood that he's more then excited to share.
The bridge of Taylor Swift's "Father Figure" but it's Bartemius Senior to his son after sentencing him to a life's imprisonment in Azkaban.
The last chorus of "Father Figure" but it's Barty to his father as he kills him, knowing that for months he'd outsmarted and deceived not only him, but Dumbledore, Hogwarts, and the Ministry as a whole
James who's usually super outgoing and sociable having absolutely no clue how to talk to Regulus's friends. He tries really hard, because those are his boyfriends friends and he wants to be friends with them but Pandora's been talking casually about spirits in the woods while Evan gives Dorcas a stick and poke tattoo and Barty bounces around the room blabbering on about a new topic every few minutes only stopping to snog Evan occasionally. He spends the night quietly sitting by himself and missing his friends, because somehow the werewolf is less scary then whoever Regulus spends his time with.