Remus slips up the stairs to the boy's dormitories by himself. Sirius had left the rest of the Marauders about an hour ago under an unheard excuse and Peter was watching James harass Lily by the lake. When he got upstairs he was surprised to see the bathroom light on and even more surprised to hear a soft crying coming from within.
He snuck over to the door, setting his books on his bed on the way over. The crying was louder now and interspersed with incomprehensible muttering. Remus tried the handle quietly and pulled out his wand when it was, unsurprisingly, locked. A quick "alohamora" and a quiet click unlocked the door and there was still no sign that the person inside was aware that he was there.
He stored his wand and with a quick shove, he opened the door revealing Sirius Black sitting on the floor, leaning against the wall. It hit the wall with a bang and Sirius looked up with a look of panic on his face. Remus didn't notice the look instead his eyes were glued to his bare arms. His usual robes or jacket had been discarded and blood dripped off his pale skin. A small knife that was also coated in deep red was clutched in his hand. Each arm sported at least half a dozen fresh cuts along with dozens if not over a hundred of cuts in various stages of healing.
"Pads..." Remus dropped to his knees next to Sirius and snatched the knife away, setting it behind him. Sirius just looked at the ground and sniffled. Remus pulled out his wand, noting the way Sirius flinched, and gently grabbed one wrist. "Shh... it's alright."
He murmured an incantation and his wand glowed softly while the cuts slowly mended themselves fading to faint scars. Sirius stared at them while he repeated the process on his other arm. He stowed his wand and pulled Sirius into his chest, holding him tight while he pressed small kisses to the top of his head. They stayed like that for several minutes, the only sound of Sirius's choked sobs and Remus's soothing murmurs. When one of them finally spoke it was Sirius, who had finally calmed enough to put together coherent sentences.
"I'm sorry, you didn't need to see that." Remus traced small patterns into his back.
"Don't apologize Siri. You don't need to apologize." He shook his head.
"I..." He sniffled. "I'm just so tired. I don't want to..."
"Shh... it's alright, I've got you now. You're going to be alright." Sirius nuzzled into his chest.
"I just want to sleep. I want... I want it all to go away." Remus blinked back tears and tightened his grip on Sirius.
"Oh Pads... I'm so sorry." There was silence for another few minutes where Sirius's breath evened out and Remus continued clutching him close. "Siri?" He shifted slightly as much as he could in his death grip.
"Mm?"
"I know... I know you just want everything to go away but... please, please don't..." He trailed off and sniffled quietly. "Please don't leave me. I love you so much and I want to help. Please just don't leave me." Sirius wriggled out of his grip, then pulled away just enough to wipe his tears away and return the hug, settling his head on Remus's shoulder.
"I don't want to leave you. You're the reason I'm still here." Remus started truly crying then and wrapped his arms back around his waist. A few moments later he took a deep breath and shifted his grip to under Sirius's thighs.
"Come on, let's get off the bathroom floor." Sirius murmured quiet assent and Remus managed to get them both off the floor with only a small struggle with Sirius still clinging to him like a koala. He kicked the knife that was still on the floor under his bed to deal with later, then shoved his books off the bed. He toed off his shoes and sat down in bed. Sirius let go of Remus long enough for him to shrug off his robes and lay down, then settled on his chest. Remus flicked the curtains closed then draped an arm across Sirius's back while he stroked his hair with the other. The raven-haired boy's eyes fluttered closed and his breathing settled into an even rhythm rather quickly. Remus pressed a kiss on top of his head and murmured softly.
"Sleep well, Siri. I'll be here when you need me." There was a drowsy whine from Sirius but he remained still.
Remus pursed his lips. He was worried for Sirius but what he said was true. He'd be there when he needed for as long as he needed. And somehow they'd get through it. They always did.