You can't handle the truth

Takes place after the scene in the barn (angels vs demons) in the episode "Heaven and Hell" season four.
Here we get to read what Castiel is hiding from Dean about why he brought him back from hell.

Dean looks as Sam turns to Ruby. He feel like his heart is beating it's way through his shirt and firmly press his hand against his chest, almost to make sure it isn't.
Sam sits Ruby down on a haystack, her body still injured from the torture earlier that night. Watching his brother being so gentle with this demon, makes Dean sick to his stomach, his head start to spin and he walks outside to clear his thoughts.

He can hear the footsteps behind him but doesn't turn around as Castiel walks up to his left.
"I know you're upset…" he starts, but is abrupted by Dean.
"What do you know? What the hell do you think you know? How can you…" Dean's panting, his heart starts raising again. He close his eyes and takes a deep breath through his nose. When he open his mouth and let out all the air in his lungs, they both watch the white mist it makes as it vanishes into the night.
"Everything…" he continues, almost in a whisper. "I have given everything." stronger this time. "I have literally been to hell and back and STILL, I haven't given enough?" He breathes heavily and for the first time he turns to Castiel. Even in the dimmed light, he could see the streaks on Dean's face, shimmering.

"Dean, we are all on different quests in this world. For you this has meant a lot of sacrifices. I understand that you are angry with the path chosen for you." Castiel says as he watch Dean quickly wipe his cheeks.
"No…" Dean says, his teeth grinding through his words. "You do not understand, can not understand because you can not feel, any of it. This is what Anna…" he points towards the barn and fight hard not to let his voice break. "This is what Anna understood, why she didn't want to be an angel anymore. She wanted to be human, to feel. And now, now she's back to being a…a vessel!" He moves closer to Castiel. "So what are you trying to tell me, that it was all for nothing? That it meant nothing, none of it does, because we're all on quests with no chance what so ever to decide our own fate?"

He continues to stare at this thing, this angel, the one who saved him from hell. When he doesn't answer, Dean starts talking again while looking down into the ground.
"When we first met, you told me you have work for me. We've met several times after that and there is something you're not telling me. The real reason you brought me back from hell, that has to be something more to it than to help you stop Lilith. Something only I could do for you, and I need you to tell me the truth." He is amazed over how calm his voice sounds and slowly turns his head back up, facing Castiel's.
"You're not ready." Castiel replies and stares back into Dean's eyes.
"Dude, I swear, I have had it up to here with your crap. There'll never be a time to be ready for any of this, so you tell me the truth dammit!"

The last word still echoing, Sam walks out to the two, wondering what is going on.
Castiel glares at him, then almost mechanically turns back to Dean and says: "Fine. I am done handling this delicately anyway. The reason we brought you back, the real reason why you were dragged out of hell."
"What? Tell me now, why am I here?" Dean screams.
"Because you're the only one who can kill Sam!"
Dean stumbles back, turns to Sam, his lower lip trembling as he's trying to find his words.
"Sam…no! No, no way! You might as well throw me back into the pit, I'd never hurt Sam, never!"
Castiel turns his back on the brothers, and just before vanishing he says in a deep voice, almost with a sigh: "You will…"

Sam's eyes are filling up with tears as his brother screams out in the dark night, a scream of despair and anger. Dean falls to his knees, beating the ground with his fists. "Why? Why me, why us? Why can't you just leave us alone? I won't hurt him, not him, not ever…" Sam walks over to his older brother, heartbroken to see him like this and terrified over what he's just heard. He puts his hand on his shoulder, Dean grabs it and sighs, such a deep sigh with all the pain that is weighing him down.

In the back stands Ruby, unaffected by what she's seeing, looking at the Winchester boys as the night seems like it will never end.