Sirius Black climbed the stairs to the third floor and stood on the landing. He could still hear Kreacher behind him snorting and sobbing outside of Regulus's bedroom, the elf's fists banging on the carpet in angry frustration, unable to do anything or retaliate against his Master Sirius. Fleetingly, Sirius might've felt a twinge of guilt, but it wasn't enough to hang on - especially once he'd reached the top of the steps and came to a stop outside of the door on the next landing. There was too much in the past, too many times that the elf's eyes had glowed through a peek-hole about two feet off the ground on that door. Sirius stared at that peek hole now... and then brought his eyes up to read the notice that had been permanently bonded onto the ornate wood.

KEEP OUT!!! NO PARENTS! NO LITTLE BROTHERS! AND ESPECIALLY NO HOUSE ELVES ALLOWED!!!!!

The letters were in big, powerful block letters, thick and wonderfully rebellious. Despite the fact that Sirius had beautiful scrawling handwriting (perfected by years of endlessly copying letters and words and long texts set before him by his blessed mother), this notice was in his messiest, all capital block letters.

He could still hear his mother's wretched howling shrieks of disapproval, which she'd let loose the day she'd come up the stairs to find the offending notice spelled onto the ruined door.

He pushed his way into the room.

It was an absolute mess. Things were strewn about everywhere, flung down upon the carpet, haphazard stacks on the desk, in the shelves, on the floors... Everything had the look of having been used, put down, and just never returned to again. The walls were covered with photographs of motorbikes and muggle women, torn from magazines and given permanent sticking charms. A few posters of muggle men were layered discreetly in - though less noticeable because they were the men riding the motorbikes or advertising the cigarettes or leather jackets or various other items that Sirius had found exciting back in the days when he was last here at this place. 

Another thing he could hear his Mother shrieking about still.

"If you don't like it, then don't come in!" Sirius recalled shouting at her, "You're already violating privacy and the  posted notice."

Sirius walked in, feeling restless and anxious already, only mere steps into the room, like an animal stepping into a trap, sensing that something was off. He scowled as he moved, eyes taking in the four walls that haunted many of his worst nightmares - the marks on the floor where the electrical current of the cruciatus had struck the floorboards or the broken bits of wood around the window frame where other curses and hexes had struck when his parents spells had missed their mark... him.

He was passing the desk when he glanced down and saw there were old bits of parchment, half written letters...

He felt the breath leave him, then, for he recognized the hand writing of the top one.

Sirius stepped up to the desk, staring down his nose at the parchment laying on top of the others on the desk, a quill set beside it.

28 March, 1979

Sirius's shaking hand gripped the back of the desk chair, which was neatly pushed in. He reached down and wish a brushing motion, pushed the quill off the page, revealing the letter beneath. His eyes swept over the length of it without reading, just taking in the imperfect cursive scrawl, and, with a twist of his stomach, the initials at the end of it.

R.A.B.

Sirius felt a lump in his throat. 

"You ickle sodcake," he whispered darkly, "Always got to be so bleeding dramatic."

He drew a deep breath, then his eyes roved back to the top of the letter.

28 March, 1979

Although I doubt you will ever return here to see this, Sirius, I want you to know that I am sorry for the things that I have done in my life, but most especially for the things that I have done to you and the things that I did not ever do for you.

I regret so much and I don't expect if I spent every breath for the next seventy years repeating "I am sorry" again and again to you that I should ever be able to make up for the hurt I've caused you.

Sirius paused here and looked away, toward the far wall, his mouth twisting into a frown. He closed his eyes and pursed his lips in frustration, letting out a low breath through his nose. 

Why did he get to apologize? Sirius wondered. Why did Regulus get a chance to apologize to him when he, Sirius, had never been given the chance himself?

He could still see that fucking stupid, ugly balloon floating half deflated in the living room at the Potter's - a fucking stupid owl with a fucking stupid I'm Sorry letter, getting more pathetic with every passing moment of uncertainty.

He could still feel the way the Potter's coffee table cut into the back of his legs as he sat staring at the fire place that night, and the sound of James's voice when they all set themselves at the table and the words your brother's gone came out of his best friend's mouth.

"Fuck you for apologizing to me," Sirius murmured, "Fuck you getting to be the one to say sorry."

Sirius wiped his eyes with the back of his hand as frustrated tears burned the rims of his eyes.

He continued reading.

I am sorry that I did not allow the hat to sort me Gryffindor when it tried.

Sirius stared at that for a moment - but he wouldn't allow himself to imagine it before he plowed forward.

If you ever find this, here are a few other things I regret having not said while I had the chance to say them:

The page ended there and Sirius reached down and nudged the top sheet of parchment aside to reveal the second... 

1. You are the bravest wizard I have ever known.

2. I admire you and I wish that I was more like you.

3. I am glad that you are my brother, even if I did not deserve you.

4. I wish that you had a better brother, a better family... and I am glad that you have the Potters --

Sirius felt his throat close up at that. He stepped back, tears blinding him, and he turned away from the desk, unable to read onward. 

The Potters. The Potters that he no longer had, whose lives had been snuffed out by the Dark Lord - the very Dark Lord that Regulus had died in servitude of. Sirius's face flushed hot and he covered it with his hands, his head swimming with unstoppable images.

"No," he part wailed and part whispered as he sank to his knees.

He could feel the darkness swirling, massing together in his chest... like storm clouds coming together to form a formidable wall of wind and violence with in him, ready to destroy all the carefully constructed barricades he'd worked so hard to build up over the last few weeks with Remus in Costa Rica.

He tried to force himself to remember the feeling of the ocean licking at his ankles, the smell of the plants wafting through their open back window, warmed by the sun... The sound of Remus's voice echoing through that little house...

But it was all washed away within seconds like a tidal wave sucking the life out of Sirius.

"Fuck off," he whispered, "Fuck off, fuck off..."

Surely you knew a few weeks in the sun couldn't drive me away?

"No..." Sirius whimpered.

Just like Regulus couldn't possibly have thought that a few pretty words on a page could erase the years of pain... Surely he knew how meaningless his apologies would be... He didn't love you, if he had things would've been different, Sirius, wouldn't they? 

Sirius shivered and hugged his knees to his chest, his forehead resting against the edge of the desktop.

"He said he was sorry..." Sirius whispered, voice cracking.

You didn't get to say sorry, so why should Regulus?

Sirius bit his lip. "Please..." he whispered. "Let me have my brother back."

Maybe if Regulus hadn't served the Dark Lord, if he'd been truly sorry and fought him instead... Maybe he would still be alive. 

Maybe James would still be alive.

James was your real brother anyway.

But you killed James Potter, didn't you?

Murderer...

Let down...

Good for nothing...

Sirius put his palm on the floor, fingers splayed, trying to ground himself, and slowly lay himself down flat on the wood. The floor was cold and hard and unyielding and awful...

And for a moment, he was back in that cell.

And it occurred to him that this room was no less of a cell.