Sirius didn't know when it started, only that it was some point in third year, but he knew with startling clarity how it had started.
Him and James had been fighting, which of course wasn't unusual, they bickered all the time. But this one was more heated. Peter had run out the moment he sensed a fight, poor boy was skittish, and Remus had stormed out after James had tried to drag him into their fight leaving the two alone in the dorm.
"Maybe if you got your head out of your arse you'd realize the world doesn't revolve around you and your quittich matches!" Sirius was practically screaming across the dorm but instead of backing down James just matched his energy, yelling right back.
"Oh and I suppose it revolves around you then? You and that fucking hopeless map project?"
"Just because you're hopless at charms doesn't mean the rest of us are." James scoffed, storming to the door.
"I don't know why your mother hates you, you're as stuck up and self obsessed as the rest of them. Fit right in. Go fuck yourself mate." Slamming the door behind him he stormed downstairs. Sirius just stared blankly at the door.
James hadn't really meant it, some part of him had known that. But how many times had he wished pain upon his relatives? How many times had he wished they were dead? Surely if he was just like them he deserved the same kind of suffering.
He turned, digging through his trunk, searching for several moments before they closed around cold metal. Pulling out the pocket knife he examined it for a moment.
Regulus had gotten it for him. He'd caught Sirius staring at a row of beautifully crafted blades in Diagon Alley before the school year and bought him one when he wasn't looking. After they'd gotten back home he'd shoved it in Sirius's hands before vanishing into his room.
Flicking the blade open he pushed his sleeve up, considering. Then slowly and deliberately he ran the blade across his arm. It really wasn't deep, no deeper than anything Mother had done to him, just enough to sting and bleed a little.
And it was facinating. He'd seen his blood before dozens of times but knowing he'd caused it to drip down his arm made him shiver. He watched a droplet trace down his arm for a few moments before making another cut, then another. Soon over a dozen small slices adorned each arm.
He almost didn't hear the footsteps on the stairs. He almost didn't get to the bathroom in time. But he did, if only barely. He shut the door just as Remus opened the door to the dorm.
"Hey Pads, everything alright? James seemed pretty angry when he came down so I wanted to make sure you're alright." Sirius froze, blood still dripping down his arms steadily and bloody knife still in hand.
"Yeah I'm fine, he's just being bloody dramatic. I'm going to take a shower and then I'll be down." That seemed to satisfy Remus.
"Alright, see you in two hours."
"Oi! I don't take two bloody hours to shower! It's not my fault that I'm the only one that knows how to wash their hair."
"Alright, alright. Fair enough." There was a moment of silence, then the sound of the dorm door opening and shutting. He let out a relieved sigh.
By time he got out of the shower the cuts had stopped bleeding and he'd run downstairs to join the group with a smirk like nothing was wrong.
Except something was wrong. It wasn't just a one time thing like he'd convinced himself it was. After a few days he'd become on edge, figity and irratable. It was like there was a phantom itch on his arms that he just couldn't scratch. Over lunch Remus called him out on it.
"Is something wrong Pads? You seem distressed." Peter piped up too.
"You're bouncy too." He shot a glare at both of them.
"I'm fine. Just a little tired." He turned his attention to his food but he could sense the glance the other three shared.
That night when the group wasn't looking he'd folded his knife into a pair of pants, then grabbed the rest of his pajamas.
"I claim the shower." James groaned.
"Great, I guess the rest of us are showering in the morning." He rolled his eyes.
"You shower in the morning anyways, fuck off." He slipped into the bathroom, locking the door behind him. Turning the shower on he let it run while he stripped his clothes off, then grabbed the knife from his pile of clothes.
By time he left the bathroom any evidence of what he'd been doing had been washed the bathroom drain.
And so it began. He quickly became addicted to seeing the blood run down his arms and then down the drain. Sometimes he made it days or even weeks before he did it again, sometimes he did it every night for months at a time.
And shockingly no one noticed. His school uniform covered the marks and showers were a convenient excuse to carry something into the bathroom and then be unresponsive for half an hour.
The only person that found out was his mother and of course she didn't care. She encuraged it actually. She'd meant to throw him across the room but only managed to rip his shirt clean off. Hundreds of thin, pale lines covered both arms and she'd grinned at them.
"I see you're finally on board with punishments. I knew it was only a matter of time before you realized you deserve the pain." He scowled at her.
"This isn't about you." Tutting she grabbed his wrist in a vice grip and twisted his arm painfully to examine them.
"Not about me? Well then. You know you're really not doing it right. If you really wanted to hurt yourself they'd be deeper. You obviously just want attention." Tears stung his eyes, whether from pain or anger he wasn't entirely sure.
"They're not for fucking attention." He was rewarded with a slap across the mouth.
"Don't speak to me like that." She twisted his arm again, exposing the veins on the underside of his wrist. "If it's not for attention then you wouldn't mind slicing your wrist. After all you won't get any attention when you're dead." He realized she had summoned a knife and was holding it out for him to take. He just stared at her, shock written all over his face. After he didn't move for several moments she tutted again.
"As I thought. Pathetic." She released her grip and swept out of the room, leaving him frozen.
His cuts grew deeper after that. Hot shower water no longer cut it and he learned spells to stop the bleeding. And still no one noticed.
When James told him that Reggie had confessed to him how abusive their parents were he should have known he couldn't keep it a secret for much longer. But he couldn't stop. He only managed to evade being checked by Madame Pomfrey for permanant injuries via an hour of pleading, three rounds of tears, and some very convincing lies.
Then James dropped the bombshell that his parents would be taking them in for the summer he knew he was fucked. And he was absolutely right. It took a grand toltal of three days for him to get busted. And it was by James of all people. He'd just hopped out of the shower and pulled on a pair of pants when James burst in like he owned the place, which Sirius supposed he kind of did.
"I'm so sorry I didn't realize you were still-" He froze, eyes fixed on the hundreds of scars and cuts on his arms. There was silence for a three count before James took a breath.
"Mu-" Sirius tackled him, a hand clamped over his mouth.
"Shut up, shut up, shut up." Sirius kicked the door shut while trying to keep James from squirming away and calling out again. Unfortunately the half scream and loud slam of a door seemed to have alerted the entirety of the house.
"James, you okay?" It was Effie and both boys froze. Sirius's mind raced. Then he hissed very quietly to James.
"I'm going to take my hand away and you're going to say you saw a spider and fell into the door. Got it?" James nodded, wide eyed, and Sirius slowly pulled his hand away.
"Sirius is hurt! Mum come in here!"
"What the fuck James?" Sirius scambled for a shirt, hurling some more very colorful vocabulary at James but it was too late. Effie had opened the door and was staring at him with Regulus at her shoulder. He was frozen for a moment, shirt in hand, wondering if there was any way to get out of the situation he was currently in. He couldn't think of anything.
So he just dropped the shirt and sank to the ground before beginning to cry. Effie quickly knelt beside him, rubbing his back gently as he hiccuped and sobbed. When he calmed slightly she brushed the tears off his cheeks.
"Let's get out of the bathroom, is that okay dear?" He nodded and she helped him to his feet. Even though his eyes were trained on the ground he noticed Regulus pick up the knife on the counter with a look of regret before he shoved it into his pocket. He doubted he'd get it back.
The group was quiet as she offered him his shirt, then led him downstairs to the couch. They sat in silence while Effie made tea, then once she returned and gave a cup to Sirius did she ask anything.
"How long have you been hurting yourself Sirius?" She wasn't mad, just calm and sympathetic which sent him into another round of tears. She didn't press, just waited until he calmed.
"Sometime third year." He mumbled it while staring at his tea so he couldn't see their reactions.
"Did anyone know?" He shrugged.
"Mother saw, assumed she told Father." That earned a dissaproving noise from Effie, a sound so similar to the one his mother had made.
"'M sorry, I didn't mean for anyone to find out."
"We're not mad dear. You don't have to apologize." James spoke, voice hesitant.
"Was your mother mad? Is that why you're upset?" He shook his head slightly.
"Don't wanna talk about it." Effie spoke gently.
"That's okay. If you don't want to talk right now that's just fine. Do you want some food? I was going to make dinner soon." He just shrugged but Regulus spoke quietly.
"That'd be wonderful Mrs Potter."
"Effie." Regulus seemed to physically cringe.
"Right, Effie." Once she went to cook Regulus settled next to him, leaning onto his shoulder.
"It's going to be alright." James moved as well, combing through his still wet hair, untangling it. He drifted off, emotionally spent and wedged between two of his favorite people. Not quite "alright" but he'd get there.