I just kinda thought of this at 3:57 in the morning and actually wrote it down and now here you all are at 5:00 in the morning. I don't normally write these little ideas I have down, but this one wouldn't leave me alone.
Sorry if it's kinda horrible :F I'm not very good at getting what's in my head down on paper*computerized paper?*.

xOx

The signs were going by faster than Castiel could read them, and at some point he just decided to enjoy the blur of lights as they drove down a deserted road.
At the speed the Impala was going, however, Castiel feared they would hit something. Or, even worse, someone.
"Dean, could you perhaps drive slower?" Castiel wondered aloud, staring out the window uncomfortably. Of course, the most Dean did was cast an angry glance towards him, saying nothing, and certainly not decelerating.
A few moments of tension passed before Castiel spoke again. "Have I done something to anger you?"
Dean glanced at him again, but not in anger. It was more of an apologetic look. "No, Cas."
"Is it Sam?" He knew he was pushing his luck by expecting an answer, but sometimes Dean managed to surprise him.
It was silent again, and Cas figured that was the end of the conversation. He was about to leave, like he normally would, when he heard Dean's voice.
"I...don't want to talk about this, Cas."
"You mean you don't want to talk about it with me. You don't think I'll understand." Brief flashes of home came to Castiel's mind, the blood his brother's and sister's were shedding, how they were all the same but suddenly split in half, fighting for God or fighting for Raphael. He wanted to laugh at the irony. If he thought about it, he was almost in the exact same position Dean and Sam used to be in; forced to fight each other for another's purposes. Except, there would be no happy ending here. There would be no loopholes. Not in the position he was in. Not with the way his family was falling apart so quickly to one brother's intolerance to a change of pace.
He looked up at Dean, eyes half-lidded in sadness and memories, and said "I may not understand completely, but I understand the pain it causes, Dean."
Dean felt like he was shooting himself in the foot. "Cas, I never said you wouldn't understand, I just...I don't want to talk about it." He looked over at the passenger seat, expecting to meet challenging eyes, but the seat was empty.
Cas had left.
It's funny, he thinks, how lonely the Impala seemed now, when it always seemed so noisy with the casual banter between him and Sam. Or how peacefully quiet it was when Cas was in the car.
When it was just him, it was deafeningly quiet, and it scared him. Dean wouldn't admit it out loud, but he doesn't want to be alone. Not ever. He allows his mind to wander on that thought, though, thinks how he'd feel years from now if Cas was gone for good, if his relationship with Sam was ruined. How lonely would he feel, then?
He ends that thought where it is, turning his music up so loud that he can't hear himself think, doesn't want to hear himself think.
He forgot where he was going long ago, forgot why he bothered trying anymore. He thinks (no, he knows) that he tries for Sam, because Sammy is all he has left.
But what good is the last apple when it's rotten?