Author's note: I needed to write this for myself more than anything. I'm missing Cas so badly, despite 8x02, and I can't wait to find out how Cas escaped, so here's my own person headcannon. I hope you enjoy it!

Disclaimer: I don't own Supernatural or any of the characters in this story, or Destiel would have been canon from the very beginning.

Promises

Dean was lying on the thin motel bed, feigning sleep. Sam was in the bathroom, brushing his teeth and getting ready for bed; Dean didn't bother anymore, just slept in his clothes and, when Sam didn't force him to take them off, his boots too. It always made him feel more comfortable, the knowledge that he could spring into action at any moment, fully dressed and ready to fight. If he didn't know it would worry Sam, he wouldn't even sleep on the bed; he preferred to lie on the hard floor with his knife in hand. Instead, he tucked it beneath his pillow, occasionally reaching out to touch the cold metal, and though he knew that Purgatory was only a memory now, it still reassured him to know that he could protect them both if necessary.

Dean jerked upright when he heard a faint knock on the door. "Who is it?" he growled, hand moving instinctively for the weapon. When he received no answer, he rose slowly to his feet, casting a backwards glance at the bathroom door. Sam didn't appear to have heard the knock; Dean could still hear the sound of running water and splashing. Dean edged towards the door cautiously, fingers wrapped around the solid wooden handle and opened the door just a fraction.

The next moment, the door swung open with a resounding crash and Dean stared, wide-eyed, at the familiar, trenchcoat-clad figure stood before him.

"…Cas?"

Castiel swayed unsteadily on his feet. "Hello, Dean."

There was only a moment of stunned silence before Cas let out a soft sigh and closed his eyes, his legs giving out as he crumpled. Dean only just managed to catch the angel before he hit the floor, hard, and helped him into a sitting position against the wall. Cas' suit was soaked with blood, and his expression was dazed. Dean hands were trembling as he pushed Cas' coat to one side, and he inhaled sharply in a breath when he saw the deep wound on Cas' side, just below his ribcage. "Shit, Cas," Dean cursed as he pulled off his shirt and pushed it against the wound in a desperate attempt to stem the bleeding; Cas didn't even flinch. He could hear Sam's questioning call from the bathroom, and then hurried footsteps.

"Dean, what's-"" Sam stopped dead in his tracks. "Cas?"

"Sam, get the kit," Dean growled, and Sam hurried away without question. Dean concentrated on Cas, on the way his eyelids fluttered and closed, and he pressed down a little harder, feeling a rush of relief when Cas hissed and opened them again. "I know it hurts, Cas, but you've got to keep your eyes open, okay?"

Cas nodded weakly, and Dean placed a hand on his shoulder, felt it solid and warm and real beneath his palm, and he couldn't stop the tremor than ran down his spine. Cas was here, with Dean, and he was alive and breathing and God, Cas is alive. "Jesus, Cas," he choked, forcing the words up around the sudden lump in his throat. "I saw..."

The memories had haunted Dean since his return; every night, in that dark, lonely place between sleep and dreams, Dean relived the moment Cas' hand slipped from his grasp, remembered how Cas had scrabbled at the ground as he was pulled away, crying out for Dean even as the door to Earth began to open. Dean hadn't been able to stop it, and in the end he'd been forced to leave Cas behind in Purgatory to die, alone and cold and surrounded by monsters and the eternal darkness. He told himself he had no choice, that Cas would have wanted him to leave if it meant he would survive and be reunited with Sam, but he knew he was just trying to ease the guilt he'd been feeling ever since he opened his eyes in that empty field with Benny in his arm and a cry of Castiel's name fresh on his lips. It never worked.

"I thought you were dead."

"Escaped…" Castiel gasped, breath hitching in his chest as another spasm shook him.

Dean's eyebrows knitted in confusion. "Benny said only humans can escape," he began, and then that's when it hit him.

Cas was bleeding.

Cas was in pain.

Cas was human.

The realisation was staggering, like a punch in the gut, and Dean held a hand against the wall to steady himself as he reeled from the blow. "Shit, Cas, what did you do?"

Dean already knew, but Castiel answered anyway. "I tore it out… my Grace…" Castiel's eyes went wide, and Dean knew that the enormity of what he'd done was crashing down on him. Thin fingers grasped Dean's sleeve, and Cas shook harder, though it wasn't the pain this time. "Dean."

"Cas, you stupid…" Dean couldn't finish the sentence. He couldn't even think about how much it must have hurt Cas to physically tear his Grace from his vessel, couldn't even imagine. And it wasn't just the physical pain, either; Dean could still remember the look on Castiel's face and the defeat in his voice as he told them he couldn't heal Bobby. Cas had hated being powerless, hated being weak and unable to help, and now it was happening all over again, except this time, he'd chosen it. Dean felt like he was going to throw up, but he swallowed the nausea down and, with some effort, turned his focus back to the angel in front of him. Cas was gripping Dean's arm so tightly now that Dean knew there'd be a bruise there in the morning, shock from his injuries rapidly spiralling into panic.

"Dean," he whispered again, and, without thinking, Dean reached forward and cupped a hand to Cas' jaw. Cas' pupils were blown wide as he stared up at Dean.

"Cas, you listen to me. You're gonna be okay, you got that? We're gonna get you fixed up, and you're gonna get through this. I promise." Dean knew how sentimental this sounded, but for once he didn't care; all that mattered was the way Cas shuddered and leaned into his palm. Dean leaned forward, pressing his lips to Cas' damp, sweat-soaked hair. "You're gonna be okay."

They sat like that until Sam returned, and then Dean pulled back and cleared his throat. Sam didn't say a word as he carefully peeled the stained shirt away, revealing the wound. Dean's stomach twisted, but Sam remained calm and professional as he began to wipe away the blood with a small towel. Cas' eyes were half-closed and glassy, and Dean could see that he was losing the battle to stay conscious. After he'd washed away most of the blood, Sam pulled a sterile needle and thread from the bag, and Dean winced involuntarily at the thought of putting Cas through any more pain, but the ex-angel was so out of it that he didn't seem to notice as the sharp point pierced his flesh. Dean didn't know when he'd taken Cas' hand, but didn't let go.

Once it was over and the wound was stitched and bandaged securely, Dean gently lifted Cas and carried him over to the bed. Cas was asleep now, a limp weight in his arms, having finally succumbed to his exhaustion. Dean set him down gently on the bed, and watched the slow rise and fall of his chest for a while as Sam packed everything away, reassuring himself that Cas was going to survive this, just like he's survived everything else that had been thrown his way.

Dean's hand found Castiel's where it lay upon the sheets, his strong fingers entwining with Cas' long, delicate ones. Sam's unspoken questions hung heavily in the air, but Dean didn't have the answers, and he was too distracted to answer them even if he could. Cas could explain it all when he woke up, but for now Dean and Sam both had to be patient.

Dean didn't know what was going to happen next. It was going to be difficult, and confusing, but Dean had promised Cas that he was going to get through this.

Dean Winchester always kept his promises.

AN: Sorry about the slightly rushed ending, but I wanted to get this up tonight! Reviews are loved and appreciated!