A/N: Okay so this is a bit different from the usual fluffy Romance/Humor fics I have clung to so ardently. No fluff here whatsoever. At all.

It was originally meant to be part of a series, but as I finished writing it I felt like the Sirius part stood out far better on its own. Plus my ideas for James, Remus and Peter were kind of lame compared to this one

Yes it is rated M because of language and sexual references, I personally don't think it's too bad, but you have been cautioned.

Disclaimer: It all belongs to JKR

Sirius was walking back from Muggle Studies alone when it happened. The moment that would change his life forever. The one decision that he would regret for the rest of his days.

No, it was not the time that he met James Potter – because there was no decision involved there. James had made sure of it, confidently walking up to Sirius alone in the compartment on the train and forcing his companionship on him without giving the astonished Sirius any say in the matter. That was just how James did things. Sirius wouldn't have him any other way.

No, it wasn't the time that they made the final decision to go through with their animagus transformations either. It certainly changed his life forever, but there was never a moment that Sirius ever regretted doing what he did for Remus. Remus, the werewolf, who was forced to undergo painful transformations each month with no one to share his burden before the rest of them came along.

Instead, it happened over Regulus. Yes, Regulus, who wasn't brave enough to follow in his older brother's footsteps. Regulus, who fell in with the Dark Arts before Sirius could scare it out of him.

Regulus, who hated sprouts and could eat a whole chocolate cauldron in one sitting.

"Hey Black!" Sirius heard someone call behind him, "I heard your parents kicked you out during the summer. What, they finally got sick of the smell of the mudbloods and blood traitors you hang out with so much?"

Sirius whirled around, wand in hand and at the ready.

Avery smirked at him, wand already out and prepared to fight. "Don't like hearing about stories from home, eh, Black?" he taunted, "I wouldn't either, apparently the filth you tracked home took your mother ages to clean out, didn't it Reg?"

To Sirius's fury, he saw his nearly sixteen-year-old brother standing behind Avery with Mulciber.

"What the hell are you playing at Regulus?" Sirius spat out, indicating the other two Slytherins with his wand.

"Reg's is playing with the big boys now, isn't he?" Avery looked to Mulciber. "Go on; show your brother what you've done. Make him proud." He nudged Regulus foreword.

Regulus's face was impassive as he slowly raised the left sleeve of his robe.

Sirius felt his skin crawl as he realized what must have happened, what his parents had let happen as soon as Sirius left their house. A deep hatred for his entire family coursed through his veins like fire, making his pulse race with adrenaline and anger. After all they had done as children together, Regulus had committed the ultimate act of betrayal: he had finally cast in his fate with the Death Eaters. Sirius refused to look at the Dark Mark that was surely burned into his brother's skin, instead he kept his eyes trained on his Regulus's face. Not even sixteen years old and already a Death Eater?

"What the fuck have you done?" asked Sirius with a suddenly dry throat.

"What you didn't have the brains to do, Black," Avery inserted, elbowing Regulus out of the way now that he has served his purpose to rile Sirius up. "Joined the winning side."

"No fucking way," Sirius said harshly, trying to keep his wand from shaking in his anger.

"Believe it Black," Avery said, eyeing Sirius's raised wand distastefully. "Your little bro has finally made it to the big leagues. And what about you, still mucking about with blood traitors and mudbloods, I see. Have you no shame? Did you know I saw your blood traitor pal lusting after that mudblood the other day. He should just up and shag her already – I bed she's never had someone that pure inside her-"

"Shut your mouth!" bellowed Sirius. "Stupefy! Impedimenta!"

Avery dodged out of the way of Sirius's spells. Instead they hit Mulciber behind him who couldn't see what was going on. Avery laughed as he saw the older seventh-year crumple behind him.

"How dare you insult James," Sirius roared as Avery fired his first spell, "He is ten times the wizard you'll ever be!"

"Clearly not, if he's chasing after filth like that," Avery spit out as he avoided Sirius's jet of orange light.

Sirius smirked. "I see how your vision of filth might be warped, with a mother like you've got, Avery. I heard you lot keep her locked up in the attic and Silence her to keep the neighbours from finding out. Mad as a hatter, they say. From inbreeding, I reckon," Sirius said, grinning as Avery's confident smile slipped off his face to be replaced with a scowl. "What? Surprised I know about your little secret? I heard things, while living at my parents' house. Things that I could spread to all your Death Eater friends."

"Are you threatening me?" Avery said in a deadly quiet voice as he sent a silent stunner toward Sirius.

The Gryffindor leapt aside and said casually, "You bet your unattractively flat arse I am. So, keep your mouth shut about my best mate."

"Only one wizard is equipped to give me orders, and that certainly is not you, Black!" Avery screamed, looking quite deranged.

"So your mum's a wizard then?" Sirus asked, faking surprise. "That certainly explains a lot."

"Regulus! Are you just going to stand there and watch him insult me?" Avery yelled, turning to Sirius's little brother who was simply standing by and watching the fight with wide eyes.

Quickly, while Avery's attention was diverted, Sirius sent a silent stunner at Avery's knees. It met its target, and Avery fell with a clatter. Suddenly Regulus pulled out his wand.

"Don't you dare curse me, Regulus," said Sirius quietly, staring intently at his raised wand.

Regulus straightened up, but his wand never deviated from Sirius's face. "What right do you have to order me around?" he asked coldly, "You lost all your rights as the older brother after you ran away."

"It's good I did. Looks like I got away just in time," said Sirius, casting a dark look at Regulus's now covered left arm.

"I made my choice, just like you did six years ago," Regulus said quietly.

"What choice was that?" asked Sirius, lowering his wand as he stared at his brother.

"To be a bloody Gryffindor! To leave us, your family!" yelled Regulus.

Sirius internally cowered, but willed his face to hide his discomfort. Regulus's words echoed in the deserted corridor, full of pain and unspeakable raw emotion. "Family... family...family..."

"It was not my choice!" Sirius said loudly, trying to block out the words that were still being parroted back at him. "The hat put me where I belonged."

"The stupid had did exactly as you asked it to! You decided you didn't want to be like us, so you weren't, and don't you deny it Sirius," said Regulus angrily.

"Fine," he said, shaking his head. "So what if I didn't want to be with a bunch of snakes?"

Regulus hissed undistinguishable words at the insult, but Sirius continued on.

"Regulus, you don't understand. I couldn't live with them anymore," he said, hating the pleading note in his voice, "They were so fucking unbelievable with all their pureblood nonsense and 'mudbloods this' and mudbloods that.' I couldn't stand it."

Regulus took a step forward, glaring at his brother. "You are so fucking unbelievable. Trying to play the hero, aren't you? We, the so horrible Death Eaters were crushing your noble spirit." Regulus laughed hollowly. "I bet that's what you told your blood traitor friend. You're so full of shit, Sirius."

"I'm full of shit, Reg?" Sirius said in a mocking tone. "I'm not the one who joined up with the Death Eaters because they were the biggest bullies in the playground."

"Stop talking about what you know nothing about!" Regulus said heatedly.

"Then enlighten me, oh brother of mine," Sirius demanded.

"Look, you ran away! You found a whole new family, but I couldn't do that, Sirius, because I already have one. And unlike you, I don't see anything wrong with it!" Regulus spat.

"Of course you don't," said Sirius condescendingly, "Because you're the perfect little mummy's boy, aren't you?"

"So what if I am?" Regulus said angrily, "They're views are perfectly legitimate-"

"They're such rubbish, even you must know that!" interrupted Sirius.

"Just because you left me-" Regulus broke off for a moment, looking angry. "Left us," he rephrased, swallowing before he continued on, "Gives you no right to insult my beliefs!"

"Well they deserve to be ridiculed," retorted Sirius, looking into Regulus's eyes, "I know more now, you know, living at the Potter's. They got things right."

"Is that so?" said Regulus with disdain.

"Yes," Sirius said firmly.

"The Dark Lord is taking over. Stop pretending that this is between you and me, it's so much bigger than us," Regulus said, forcing himself to be calm.

"Bullshit. This is because of your ridiculous desire to be the perfect son!"

"Because you so obviously failed in that respect!" Regulus shouted, completely losing it.

"Newsflash, I don't want to please Mum anymore! She can go to hell for all I care," Sirius fumed.

"Take that back," Regulus said quietly as he stepped closer, wand still out and pointing at Sirius's chest. "Take that back," he repeated, giving Sirius an icy glare.

"No," said Sirius defiantly. "All their theories are a load of tosh, and you were a stupid twit for joining up."

Something hardened in Regulus's eyes. He raised his wand, but Sirius was faster.

"Adflictum," he shouted, whirling his wand on Regulus.

Sirius watched with a crazed sense of accomplishment as his brother was knocked off his feet and thrown a little ways down the hall. After all, what right did Regulus have to say those things to him? Sirius thought he left all those things behind, that excess pureblood baggage, when he ran away last June. Trust Regulus to not let it go and bring it all up again. It was his fault really, for not respecting his elder brother's decisions.

Sirius confidently walked over to where Regulus was laying, completely ready to unleash a sentence or two of triumph.

The words died on his lips.

All Regulus was doing was looking at him, and everything, every vestige of anything, fled from Sirius's mind. Only a dirty cloud of shame and guilt swirled in his head, making all other feelings impossible. Regulus's dark eyes were filled with such emotion that Sirius was dually mesmerized and horrified. How could he have not seen it before? He must have been blind because he saw all laid out to bear in that instant. All Regulus was feeling was, at last, conveyed in to his elder brother.

The surface was most obviously filled with anger and humiliation. But there was something deeper, something that Sirius didn't want to face. It made his lower stomach clench in discomfort and hands shake in revulsion. Sirius hated it, this physical reaction to the guilt that was piling higher and higher on his shoulders as Regulus continued to hold his gaze.

When he left last June, Sirius knew it was a drastic move, but he was certain that he could not remain in 12 Grimmauld Place a minute longer, surrounded by the beheaded elf heads and his mother's the angry looks. He needed to be free, to get out and see the world to know that it simply existed outside of his prison. It was more than a desire, it was an obsession. He Needed To Get out. Now.

So Sirius left, taking a few of his belongings with him, and leaving the majority everything he had ever known behind.

Including his little brother.

And it was this brotherly betrayal that was shining out of Regulus's face. It cut deep into Sirius, and made him, for first time in practically a year, question if he did the right thing by leaving. If he should have stayed there for his brother. For Regulus.

But then Regulus blinked, and the spell was broken.

Mad and confused, Sirius, at that moment walked away. That was it; he just put one foot in front of the other in the vain hope that a physical distance would be enough to spare him from all he was feeling.

He didn't go back to confront Regulus again.

He didn't go back to talk to Regulus.

He didn't go back to reason with Regulus.

He never once looked over his shoulder on his way back to the Gryffindor Tower.

It was only as he sat down in his scarlet and gold bed that Sirius Black realized the wetness on his cheeks were tears.

For some reason this made him angrier than ever. Even as his pulse raced with hatred for his family, the water still continued to leak from his eyes. Stupid little brother was making Sirius question every so called good decision he had ever made.

Should he have been sorted into Gryffindor?

Should he have struck up a friendship with James Potter?

Should he have run away from home?

The heap of regret and hatred was making the tears come faster. Because he couldn't deny it, Sirius now regretted not going back to make amends or at least helping his brother to his feet. He could not convince himself of otherwise. There was no justification to his actions. Regulus, for all his annoying pureblood nonsense, did not deserve to have a brother who abandoned him at a moment's notice. Sirius felt sick to his stomach as he pictured Regulus alone with his parents in that fucking depressing house for practically two whole months. Nobody deserved that fate. Not even Regulus. And now Sirius could've gone back, resolved loose ends with Regulus and tried to protect him like an older brother should, but he didn't. Instead he abandoned him once again. But not into the protective hands of his pureblood parents, instead Sirius left Regulus to fend for himself among the infinitely worse Death Eaters. A fucking million times worse than his parents.

At that moment, for the first time in his life, Sirius realized that he had made the worst decision in the worst possible situation.

Little did he know that he would, all too soon, be feeling this same overwhelming, heart breaking, all consuming regret once more before his life was over.

And that would be the night of October 31, 1981.

It was only as he heard a shout of laughter coming from the common room downstairs that Sirius realized that people, his friends, were going to come up here and find him sometime soon. By his estimate, dinner was just about over. Well, he wasn't going to let James take the mickey out of him for bawling like a girl. He wiped away all signs that he had been crying and swept out of the dormitory like a man on a mission. Obviously Sirius didn't know what he wanted, what he was feeling, or what he should do. He acted on the first impulse that came to his mind. He resolved to make someone feel even worse about themselves than he did at that moment.

And so that was why, that fateful full moon when Sirius was sixteen, alone, and miserable, he went out to find Severus Snape and tell him exactly what he wanted to hear.

A/N: It just goes from bad to worse, doesn't it?