Sirius didn’t mean to leave Regulus alone. It had just happened. It was all a huge mistake, and a misunderstanding. It all started with a stupid fucking arguement, one that Regulus wasn’t meant to get involved in at all. So, Sirius took it to himself to pack their things and leave. The only problem was, Regulus refused to go with him.
Blame Sirius’ naivety for thinking it was just Regulus being stubborn.
With a heavy heart and bag, Sirius stepped into the floo without a single glance back. Christmas break was only a few more days, anyway. Even if Regulus didn’t feel comfortable coming to the Potter’s, he would still get to talk to him at Hogwarts. Now, it had been a couple days since he had heard from Regulus. He had sent multiple letters through an owl Sirius knew even his mother wouldn’t recognize. He knew Regulus had seen them. Yet, he still didn’t get a response.
Six days into Regulus’ silence, and they were back at Hogwarts. Sirius had been looking everywhere for even just a fleeting glance of him, just to know that his little brother was okay. He didn’t get to see him until the feast that night, and Regulus looked… fine. Completely and utterly fine, which confused Sirius greatly. He was laughing with his stupid friends, Barty and the lot.
Regulus didn’t even glance at his direction once.
It had now been 10 days since the argument, and along with the heavy weight of guilt upon Sirius’ shoulders, he had the nagging worry in the back of his mind about Regulus. Regulus still hadn’t looked at him, and yet Sirius saw him all the time. Even James and his friends couldn’t make him smile. He knew that Regulus would be upset, but he didn’t think that after this Regulus would still choose their parents' side. Sirius couldn’t accept that, because fuck that.
Sirius had been more of a parent than their mother and father could ever dream of. He had been there for Regulus, and being shoved to the side now felt like being stabbed. Sirius was stubborn. He wasn’t going to give up. He left little notes in places he knew Regulus would find them. In his favourite spot in the library, where he sat in the courtyard, anywhere he knew Regulus would be.
I’m sorry.
Can we talk?
Or even just a simple, please. Sirius was desperate at this point. He just needed to talk, to explain. All Sirius did was break and ruin the people he loved, and this was a prime example. He never wanted to hurt Regulus. He was his brother after all, and yet he felt just like his mother. Every single thing Sirius touched broke, and no matter how hard he tried he could never fix it. But he had to believe he could fix this. He could. He wouldn’t give up. The honest truth was he couldn’t give up. He didn’t deserve Regulus, and he knows that, but he wanted him back.
Why couldn’t Sirius have one happy thing without it going wrong?
Just before the argument had happened, Regulus and him were laughing. They were talking about running away and living together, happy and far away from their parents. ‘Brothers forever,’ Sirius had promised. And he ended up breaking that promise, accidental or not.
He knew their relationship was severed the moment he saw Regulus set his note on fire without a simple thought. He didn’t even think Regulus knew he was there, and that thought stung more than anything. So, Sirius slowly began to give up. He sent less and less until they just… stopped. He began smiling more, but it was mostly to just put up a front. He didn’t want James and the others to be too worried anyways. He was fine.
All he had to do was convince himself and act happy and eventually he would be. He began setting his jaw and forcing himself to stare at Remus during mealtimes so he wouldn’t have to watch Regulus with his friends. He now knew what Regulus felt about being replaced with friends, and it wasn’t a pleasant feeling. He wanted to apologize, even though he knew he would never be able to get Regulus to listen. But still, he dreamed of it.
He also promised Regulus that he would never hurt him, but it seems he wasn’t capable of keeping that promise either. He kept the ring that Regulus had given him for Christmas the year before, and turned it around his finger each time he missed him. It was a bit too small, but Sirius found he liked the pain. He felt he deserved it. He deserved it after everything he had put everyone around him through. It was the least he deserved.
No matter all his friends' reassurances, no matter the many teary nights spent in Remus’ bed, no matter how many gifts and letters from Monty and Effie, Sirius never truly got better. Regulus was a part of him, and he got violently ripped away from him, making it impossible to stitch them back together.
So, time passed but the seam between Regulus and Sirius never began to heal.
After all, it is the destiny of stars to collapse.