Regulus answered him with silence. Silence and a half-open mouth that wanted to speak but could not form words. He was being careful not to exacerbate the situation but, Merlin, he had no idea what Sirius was thinking, anyways.
“I want—” he wavered where he stood, halfway between approaching his brother and remaining hovered by the door, “I want you to… think about what you’re doing. You can’t undo a decision like this. You know she won’t let you.” Sirius had to know where the choice would lead him—permanently, irrevocably removed from the family.
From him.
“You’re angry, and upset, and emotional, and you know there can be no logic here. You’ve been—influenced, by those people. By your friends, and…
“Sirius, you can’t leave.”
"Oh, I can't?" And he whipped around, all the anger and fear he's not allowed to show in front of Walburga or Orion now on display in force.
The hand around his wand was shaking, and he dropped the wand into his trunk to really keep himself from doing something he would regret. He knew, without a doubt, that he'd end up cut off. Like Uncle Alphard. Like Andromeda. No contact without reprimand. Or worse. This could be the last time he would see Regulus without house colors draped over him.
And even then. Walburga had eyes and ears everywhere.
"I'm not going to let her bully me into moving with Bellatrix. She clearly thinks she's failed as a mother and --" That's fucking rich, honestly. Perfect.
"Fuck her. I can't take this shit anymore, Regulus."