Regulus wondered to himself worriedly, Will this be the last straw for him? Sirius had fought with their mum and dad since he was old enough to shout, and every summer it was the same.
During the school year, Regulus and Sirius were mortal enemies, acknowledging each other only with hexes and insults and deathly grey glares. But over the summer, they were each other's only allies. Not that either of them would admit this to any of their friends. Regulus's Slytherin counterparts would never forgive, and Sirius's Marauding mates would never understand.
At home, though, with mum and dad always screaming at Sirius and always expecting the world from Regulus, the two brothers were best friends, the only reprieve from the horror that was Number Twelve Grimmauld Place.
But Sirius had been threatening to run away for weeks. Ever since the start of summer when Mum and Dad told him he'd be cut out of the inheritance if he didn't clean up his act. And ever since then, Regulus had listened to every argument with breath held, crossing his fingers that Sirius wouldn't run away just yet. That he'd stay with Regulus just a bit longer.
The screaming had temporarily ceased, and Sirius stormed up the stairs. Regulus counted the steps - would Sirius go to his bedroom and start packing? Or would he come to Regulus's door as he always did after one of their rows? Five steps. Regulus gasped. Sirius was going to leave.
A pause. Then six steps more. Regulus breathed a sigh of relief as the door slammed open and his disheveled brother stormed through it. He put down the magazine he'd been reading and met Sirius's grey eyes that were so full of hurt. Sirius climbed into his brother's bed, and Regulus ran a hand through the dark hair that so mirrored his own. Regulus could see tears shining in those beautiful eyes.
"I thought you were going to leave this time," whispered Regulus.
"I thought so, too," Sirius replied.
"I don't know what I'd do without you here," Regulus said quietly.
"That's why I'm staying," said Sirius.
And with that, Sirius leaned in and pressed his lips onto his brother's. Regulus closed his eyes and sighed. It had always been the comforting relationship, but it hadn't always been one quite like this. Only this summer, the summer before Sirius's last year at Hogwarts and Regulus's sixth. The first night this summer when Sirius stormed into Regulus's room, Sirius had reached down and grazed his brother's crotch with his hand. Ever since then, it had been this way.
Regulus let himself be kissed, let Sirius's tongue explore his mouth, hard and fast and full of anger and passion. He let out a gasp when Sirius's hand found his crotch and began to massage gently. And even though it was so wrong to be doing this with his own brother, he couldn't help that it felt fucking incredible and that he'd never even gotten to do anything like this with anyone but Sirius, and himself. Sirius was fumbling with his belt now and reaching down to find Regulus's half-erect cock, and he began pumping it viciously. Regulus whimpered and felt that he might come already, but he willed himself to hold back so he could savor this amazing feeling for as long as he could.
Sirius had now pulled Regulus's pant down and tossed them to the ground, and his own trousers were down to his knees as he struggled to a kneeling position. Regulus obediently flipped onto his stomach and felt Sirius lean down over him, strong hands reaching up under his shirt to caress his body. A whispered spell sent covered his entrance with cool lubrication, and then he felt his brother.
It didn't really feel good but it felt good to Sirius, and Regulus loved making Sirius feel good. He could hear his brother's grunts and loud breath against his ear, and Regulus fought to keep the thoughts of how wrong it was away. He was making his brother feel better. He was making his brother stay at home instead of running away to some Blood Traitor's house. He was taking his brother's cock in his arse and now it was brushing against that spot . . .
Regulus cried out. He was thrusting against the mattress now, in time with Sirius's thrusts so that his arse met Sirius's hips with a loud smack. Sirius's cock was harder now; his brother was about to come. Regulus fought to hold on as long as he could, for sometimes if he wasn't finished when Sirius was finished, his brother would take his cock into his mouth.
Don't think about that or you'll come already, Regulus scolded himself.
Sirius's hand grabbed Regulus's dark hair and pulled, and Regulus was distracted from the intense pleasure for a moment by the sting of Sirius's strong grip. With three rough, hard thrusts, Sirius froze, shuddered, shivered, and emptied himself into his brother.
Regulus hadn't come yet. He hoped and prayed that Sirius would suck him to completion. Sirius rolled off of him and Regulus turned over, exposing his rock hard erection that sprung up and rested on his belly.
Sirius stared at it for a moment, as if he were pondering what to do. Regulus was waiting, holding his breath, hoping for something . Sirius's eyes darkened.
"Fuck me," he instructed fiercely.
"What?" Regulus stammered.
"Fuck me," spat his brother.
Sirius grabbed Regulus roughly by the arm and pulled him up onto his knees. Sirius tugged his jeans all the way off and tossed them to the floor before lying on his stomach, his arse tilted up into the air.
Regulus was frozen to the spot, unable to move, in shock.
"I said fuck me, damn it!" said Sirius.
Instantly, Regulus moved between his brother's legs and with a shaking hand, guided his cock to his brother's entrance. He was about to push forward when-
"Lube," said Sirius.
"Right," Regulus replied nervously.
Sirius cast the spell himself. Regulus had never done this with his brother before. What did it mean? But now, Sirius's hole was glistening with wetness and Regulus's cock was twitching madly in anticipation. Regulus positioned himself and pushed forward, hard.
Sirius gasped and so did Regulus. Merlin, he'd never felt anything so hot and tight in his life. His own hand couldn't compare. Hell, Sirius's mouth couldn't even compare, and he had thought that mouth was heaven itself. But this hot, tight, brilliance was beyond imagination. As Regulus looked down, he realized he hadn't even thrust all the way in yet. He pushed forward again and saw that Sirius was gripping the sheets so hard his knuckles were white. Regulus felt a jolt of ecstasy roll through his body.
He pulled out and thrusted forward again, once again shivering with the pleasure of his brother's tight body, letting a strangled groan pass his lips. It took so little time that Regulus was almost disappointed when he felt the unstoppable orgasm that had built in him for so long, but the feeling of spilling his come into his brother's arse was overwhelming. His cock twitched its pleasure once more, and Regulus pulled out and collapsed onto the bed.
The next day, Sirius was gone. Mum and Dad screamed some more. And this time, Regulus had no big brother to join him in his bed afterward.