Not his brother anymore
September 1972
Regulus is standing by the door, trunk packed waiting on Sirius. Regulus is excited to go to Hogwarts. Excited to get away from his parents, excited to spend time with Sirius.
However his excitement comes to an end when his father walks in with his cane, Regulus knows what it means when his father walks with his cane. Someone has made him mad, and by his face, he is surprised to see it was himself. Orion walks over and before Regulus can even think to say something his father is hitting him with the cane mumbling nonsense about Gryffindor and disgrace.
At that moment in time, Regulus wonders if his father thinks he is Sirius. Then it clicks he’s beating the Slytherin into Regulus; so he doesn't dare think about being sorted into any other house but Slytherin. This goes on for a few more minutes, Regulus holding in his tears just sits and takes it like he’s been taught to. When his father has decided enough was enough he stands and hears Sirius walking down the stairs, once he makes it to the bottom they apparate to Platform 9 ¾.
Their parents are not one for sentiment just send them on their way; without a goodbye; or a smile. Regulus still hurting from the beating his father gave him just takes his trunk and walks to the train. Finding the first empty compartment, nothing on his mind but just getting as far away from his parents as possible, Regulus doesn’t see Sirius the whole train ride.
He doesn’t see Sirius again until the sorting ceremony, the ceremony where the sorting hat screams Slytherin. And Regulus well he's not exactly upset, he knew what would’ve happened to him if he was sorted into any other house.
But the look on Sirius’s face told him everything he needed to know he had just lost his brother. He can't help but wonder why. they both knew he would be sorted into Slytherin, so why now has he decided Regulus isn't his brother anymore?
He doesn't have much time to think about it before the feast starts, and then Narcissa leads him to the dungeons leading him to his dorm room, where he finds two other boys he somewhat recognizes. When they tell him their names his face fills with recognition.
"I'm Evan Rosier," The skinny blond boy with paper-white skin and barely there freckles says. "And I'm Bartimus Crouch, but you guys can call me Barty." The boy with brown hair and slightly tan skin says. At that moment Regulus knows his brother might not want him but these two boys sure as hell seem to want him. And in some sick and twisted way, Regulus knows he wants them too, he might not admit it until well into his 4th year but he knows within the first 5 minutes of knowing the two boys they will be his rock when the world crumbles under him.
Regulus doesn't know whether to be relieved or terrified.