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Reminder: Happily ever after NOT included. Bail now if that's not your cup of tea!

Disclaimer: Much as I would like it to, Supernatural does not belong to me.

"Promise me you'll kill me when the time comes."

Dean's words cut through the air like shrapnel and buried themselves deep in Castiel's heart. The shock of pain left the angel momentarily breathless. With shaking hands, he placed the box of files he'd been carrying onto the stack to be returned to the archives. Carefully composing his face, he turned to see Dean watching him closely from the doorway of the library.

The man was haggard from the ever-growing strain on him, but he seemed completely calm. In the two weeks that had passed since Dean had stopped Castiel from leaving, they'd found no further leads to follow in their search for a cure. All four of them were exhausted and irritable, Sam in particular. But still they pushed on. As he'd agreed, Dean was trying hard not to give up, but hope was wearing thin for them all.

"Dean..."

"I mean it, Cas. Please don't let me hurt anyone else." He spoke firmly, and the eerie serenity of his manner set the angel on alert.

"What's wrong? Why are you asking this now?"

Dean's mouth stretched in a smile that didn't touch his eyes. "Nothing's wrong that wasn't wrong already. I just need to know I can count on you to do that for me. I can't ask Sam – I couldn't put that on him. Plus the Mark won't let me go easy. Since you're juiced up again, I'm pretty sure you can kill me and make sure I stay dead."

Something deep down inside Castiel went crackling, icy cold.

Despite his fears about the whole dire situation, it'd never truly hit home that they might fail. They'd prevailed in far more difficult predicaments. But what if they couldn't this time? The possibility that Dean might actually succumb to the Mark's power was suddenly horrifyingly real. If that happened, he would be lost to the angel forever.

He turned his back and clutched at the bookshelves to keep from sinking to the floor.

Since that night on the stairs two weeks ago, Castiel had stayed with the hunter, forcing down his own fears in order to be whatever Dean needed – moral support, a sounding board, a shoulder to cry on. He was sick with terror and heartbreak, but Dean needed him, so he soldiered on. But this? He couldn't do this.

"Cas?"

Dean's rough voice in his ear brought him back out of his head. The hunter was steadying him with one hand on his shoulder and the other at his wrist.

"Come on, man. Let's go sit down before you fall down." The words were gentle and soothing and they did absolutely nothing to thaw the icy fear in Castiel's heart.

Dean guided him away from the shelves and over to one of the couches, settling him at one end and sinking down beside him. Castiel stared down at Dean's hand still at his wrist. It was so different from his own hand – broader, more tanned, and rough with fading calluses. It bore barked knuckles, nicks, and many long-healed scars. It was beautiful. Soon Castiel wouldn't be able to compare them for those little differences. Soon Dean would be dead by the angel's hand.

Dean lifted his hand to Castiel's chin, turning him to examine his face. "Hey, buddy, what just happened?"

A different kind of pain filtered through the haze. Buddy. Dean's buddy. His pal. Just the kind of friend you can ask to murder you.

Castiel closed his eyes and shrank away from the hunter's touch, tension thrumming through him. "Please, Dean. You can't ask this of me."

Dean sighed and sat back a little on the couch. "Cas, if there was any other way, you know I'd take it."

The angel leaped to his feet and snatched up another box of ancient manuscripts. "There is another way. We'll find a cure. We just have to look harder!" He thumped the box down onto the heavy oak table in the middle of the room and dug through it.

"We're looking, yes, but we're running out of time. It's getting close, Cas – I can feel it. I need to know you won't let me hurt more people." Dean had followed him to the table.

Castiel shook his head, trying to shut it all out. "Dean, no. No."

"I need you to do this for me. Cas, please." Dean reached out to grip his shoulder.

"I can't!" All through the bunker lights flickered and sparked as Castiel snapped. Power surged through his body as all the fear and pain he'd been tamping down coalesced into a blinding rage. Glass from the fixtures above them exploded into a glittering rain.

Castiel lashed out with his power, and the built-in bookshelves he'd clung to for support moments ago tore away from the walls and splintered across the floor, books and papers scattering everywhere. The act of mindless destruction felt incredibly good.

He whirled around to snarl in Dean's face. "I already have to stand by and watch you die! You can't make me be the one to kill you!" Howling the last words, the angel grabbed the edge of the table and flung it into the far wall, narrowly missing the hunter and leaving the furniture as so much plaster-dusted kindling. He was dimly aware that Sam and Charlie had come running, weapons and flashlights in hand, but Dean waylaid them at the door, reassuring them that he would handle it.

Ignoring them completely, Castiel continued venting his fury on the room, upending furniture and smashing walls until he was reduced to tearing apart individual books. When the rage finally burned itself out, he was left sitting limply in the middle of the destruction, breathing hard and shaking with grief for the man he hadn't even lost yet.

Dean approached cautiously and sat beside him in the debris, wrapping his arms around the angel. Castiel leaned into the embrace, pulling his hunter closer with fists bunched in his flannel shirt. Dean rocked him gently as they clung to each other in the dark.

"Cas? You okay?"

Castiel made a rude noise. "No, I'm not okay. I'm anything but okay."

"Right. Sorry." Dean at least had the decency to sound contrite.

They sat together a good long while, neither of them making a move to get up. At one point, Sam and Charlie peeked back through the doorway, but Dean waved them away so they were alone again. Castiel was grateful. He just wanted to be held by his hunter for a little while longer.

"I'm so sorry, Cas. I should have realized how hard this is for you," Dean murmured. "You've been covering it so well, I didn't know. I'm sorry."

Guilt nudged into the aching sorrow. "I didn't want you to worry."

Dean laughed a little sadly. "You shouldn't use me as an example of how to deal with your feelings, you know. Sammy's always told me bottling everything up ain't healthy."

"Apparently not."

"Do you at least feel a little better? I always feel better after a good tantrum."

Scowling into Dean's shirt, he considered snapping at him again, but instead settled on the truth. "A little, yes."

The hunter's palm rubbed up and down Castiel's back. "That's my angel."