Skipping a few episodes here. I'm really just going by what episodes have inspired me so it could end up being pretty sporadic.

S4Ep16 On The Head of A Pin

Castiel hated to ask this of Dean, hated to ask anything of Dean right now, really. Dean was hurting, and angry, and his words had a certain bite to them. And Uriel was not helping. Castiel really wished the other angel would choose his words more carefully. And to tell the truth, Castiel was also still bitter about Dean's affair with his sister, which was unfair to Dean, Castiel knew, but he couldn't seem to put a lid on it.

Jealosy, it seemed, was a new and frightening beast. But all that anger and bitterness was outshone by sympathy and regret when Dean realized what it is the angels were asking of him. And Castiel had never felt more helpless than when Dean had turned to him and asked not to have to do this, and there was nothing Castiel could do to stop it. This was non-optional.

Castiel did his best to do as his superiors had ordered, to remember to whom his loyalties lay. They had been right to accuse him of becoming too close to his charge, and while he tried his best to behave as they wished, it seemed "feelings" were not like a tap one could turn on and off at will.

Dean didn't want to torture, but he did when they gave him no choice. It was clear Dean had learned well, and equally clear that he hated himself for it. And Alastair's words cut just as much as Dean's knife. Castiel wanted to pull Dean out of there. Then the Devil's Trap broke and all hell broke loose.

Castiel sat with Dean in the hospital, waiting for him to wake up. He wasn't supposed to. He wasn't supposed to doubt either, but he couldn't get his sisters words out of his head. Dean began to stir then, and Castiel decided to save his doubts and dark thoughts for later.

"Are you alright?" Castiel asked.

"No thanks to you." Dean shot back. Castiel's heart clinched. There was no telling Dean how guilty he was over the hunter's injuries. So instead Castiel told Dean about Uriel, and then Dean asked the one question Castiel was not looking forward to.

"Is it true? Did I break the first seal? Did I start all this?" Castiel wanted to assure Dean, that no, he didn't. He was guilty of nothing, but figured honesty was the best policy.

"Yes. When we found out about Lilith's plan for you, we laid siege to hell. We fought our way to get to you, before you-"

"Jump-started the apocalypse?" Dean interjected, and Cas looked heavenward for support.

"But it was too late."

"Why didn't you just leave me there?" Dean asked. I could never, Castiel thought.

Instead he said, "It is not blame that falls on you, Dean. It's fate."

"You have to stop it."

"Lucifer?" Dean breathed.

"The apocalypse? What does that mean?" Castiel could hear tears behind Dean's voice.

"Our fate rests with you." The angel said.

"Then you guys are screwed. I can't do it, Cas. It's too big.

Alastair was right, I'm not all here.. I'm not.. I'm not strong enough. Well I guess I'm not the man neither of our dads wanted me to be. Find someone else.. it's not me." Tears spilled over Dean's eyelids as he let them fall shut, exhaustion and hopelessness clear on his face.

"Dean." Castiel reached out and took hold of Dean's hand. Perhaps a bit too rough, if Dean's slight jerk in the opposite direction said anything about it, but physical contact was something Castiel had yet to get the hang of. He curled his fingers around Dean, careful to keep his strength reined in, Dean was hurting enough.

"I know it's hard, and I know how much is expected of you, but no one ever said you had to do this alone. I will assist you." Castiel said, "And your brother, Sam will stand with you, I'm sure. You don't have to do this by yourself."

Deans lips twitched upwards in a ghost of a smile and Castiel echoed the expression. The angel stayed until Dean had faded off to sleep, his hand curled tight around the hunter's. When it was time to leave Castiel brushed his lips over Dean's forehead and let his Grace whisper over the human's skin, knitting it back together again and banishing the physical pain. Castiel brushed his hand through Dean's cropped hair, ensuring a peaceful nights rest, and flew off to find his sister.