Because I don't trust you.

"Come on reggie don't you trust me? I'm your big brother? Come out the cupboard mum and dad can't get you." A six year old sirius asked little regulus. That day regulus had had both French, piano and ballet after school so he was exhausted and made a mistake on the piano, hed been punished by being locked in the cupboard. It took Sirius 2 hours to get him out.

***

"Regulus please do the homework our tutor set. It's worth it don't you trust me?" 6 year old Regulus did not trust Sirius whatsoever but he still did the homework. It was mathematics which he didn't mind. He sat at their shared desk in the library and worked for hours.

***

"I don't trust you" Regulus said angrily to Sirius. 

"I promise black people and brown and every colour are all the same." Sirius had gone of to hogwarts school of etiquette and merlin this year and met his best friend James, who was Indian, and had started the process of unlearning the race superiority taught by their parents. He'd even started picking up words of Hindi. Regulus wasn't as easy to convince.

***

"James is a better brother then you will ever be!" Sirius shouted spitefully. He'd made plans to run away the next week. Regulus was having none of it. They fought and in the process bloodied an antique rug, broke a chandelier and broke off their bedroom door, "trust me, anyone, hell even Snivellus would be better than you." 

Regulus turned around and stormed out after that ordeal. He righted his clothes and hair and got ready for family meal time as usual. After a long, awkward dinner he sent a letter to his best friend Barty,

Barty,

I don't trust sirius. He says he's running away? Not only that but he's running away to an Indians house. 

Anyhow, how's Evan and Pandora. Is she still asking me to avoid water? Silly girl. 

Mother is most annoyed at Sirius and I for skipping piano the other week. 

Sorry elephants not dance, feel outstandingness of drama. 

Signed,

Regulus Arcturus Black.

***

Regulus spent his 16th birthday alone. The 'party' would be the weekend after so that the Riddles could come. The party in question would be adults talking shop and or shit for hours. 

He got notes from Sirius saying "don't trust Riddle, Reg." He simply sent back. "I don't trust you."

***

At 18, Regulus died trying to stop someone from killing another. Tom Riddle started a campaign to eradicate people of colour, which he happily joined, until he saw sirius have to defend James, his brother from his aunt Bellatrix. Next time a fight happened regulus tried to help. He successfully killed bellatrix but was shoved into a nearby lake and was held under by someone named Peter Pettigrew. When fighting him and Sirius had shared a spiteful and cruel argument.

"Reg we can defend ourselves for fucks sake!" Sirius has shouted from his place in the 'feild' after realising Regulus wanted to help, "go away!" 

"I don't trust you Sirius." And with that he died.