Castiel hasn't told anyone.
But it's time.
He's leaving.
Returning to Heaven is not something he wants. He wants… Well, what he wants he cannot have. And his wants do not matter.
Things have been relatively calm after Chuck and Amara left. The angels contained Lucifer while he was out of a vessel. It probably won't last, but it's better than him being out.
And things have returned to normal. Or as normal as things will ever be.
Sam and Dean are continuing to Hunt. The day after Chuck and Amara left, Sam called a woman named Eileen. Dean explained to Castiel how the two "had chemistry" on a previous Hunt. Castiel met Eileen soon after and immediately liked her. She compliments Sam perfectly, and Castiel has never seen Sam this happy before. Hunting with Dean and Eileen has made Sam truly content with his life.
Dean's even met someone. Her name is Heather. And she is amazing.
They met her on a Hunt just over a month ago. Dean flirted with her, and she flirted right back. She has a brilliant smile and dark wavy hair. Her blue eyes sparkle whenever Dean tells a joke. She's been a Hunter almost as long as the Winchesters, and that makes it easy for Dean to relate to her. They actually have quite a lot in common; they like the same movies, they have the same taste in food, and they are great Hunters.
She's nothing like Castiel.
And Castiel is jealous.
But not in the bitter, envious way. He is jealous in a wistful sense. He can never have what she has with Dean, and he will never have the trust Dean gives her. He cannot hate her for it, but he wishes he has what she does.
Besides, Castiel isn't blind. He sees the way Dean looks at her. She makes him happy. Castiel cannot hate anything that makes Dean happy.
Castiel remembers when he didn't understand what the term "third-wheeling" meant and how it could possibly be a bad thing. He does now. But he supposes he is technically fifth-wheeling rather than third-wheeling since he is on the outside of two relationships.
And it's horrible.
He likes spending time with his friends. Dean, Sam, Eileen, and even Heather. They all get along well, and Castiel likes them. But there is (obviously) a bond between the couples that Castiel isn't a part of. And that's how it should be. But that means he often feels like the odd man out. Castiel tries his best to be happy for his friends. And he genuinely is. But every time he sees them kiss, especially Dean and Heather, it's a reminder that this is something Castiel doesn't have. And never will.
Castiel's only ever fallen in love with Dean, and now Dean has someone. Castiel knows he never had a shot with Dean; that was never in the realm of possibility. But Castiel knows he will never fall in love again. He's not quite sure how he knows—and sometimes he feels as if he's being dismissive of potential future love—but he cannot imagine anyone else doing to him what Dean does. And it hurts. Especially when he's constantly reminded by his friends' relationships how great having something like that with someone you love is. It's not on purpose; it's never on purpose. But it's a small reminder whenever he sees Sam and Eileen holding hands or Dean and Heather cuddling on the couch that he will never have those things. And that's fine. It is. It just makes Castiel sad sometimes. But he can manage that.
And Castiel isn't the third (or fifth) wheel all the time. Castiel hasn't ever had this much free time before. There is no looming apocalypse, and Castiel has spent his extra time to try and discover who he is. He travels around the country while the Winchesters Hunt. Sometimes he picks up odd jobs. Other times he sneaks into hospitals and heals people. And he occasionally finds a park and wanders around for the day.
It's freeing and enjoyable. Castiel feels like he should be busy, and he has to keep reminding himself that he has the time to relax now. And that's it's okay to relax.
But his time in self-discovery has only proven he doesn't belong here. Sam and Dean are moving on with their lives. Humans are dynamic. Angels are static. Castiel increasingly feels as if he's watching Sam and Dean through a window rather than being in the room with them. And that's okay. Castiel never wanted to watch the Winchesters die while he was forced to continue to exist on Earth without them anyway. Now he won't have to.
The idea to return to Heaven crosses his mind almost every day in his travels. He doesn't want to leave the Winchesters. But they don't need him anymore. Heaven does. It's still a mess, and it's his fault. It's time to return and help fix all he's done.
But he also knows how the Winchesters will react. They won't want him to leave. They don't see how they're moving in different directions than Castiel. Or, rather, how they are moving and Castiel isn't. They'll tell him to stay, but that isn't what's best for them. They need to move in this new direction without Castiel holding them down like an anchor. Undoubtedly, they will be upset when he never returns, but Castiel knows they will eventually move on. It's time.
They're all seated in a diner after the final day of their week-long hunt. Castiel watches as Eileen teaches Sam new words in ASL, laughing at his mistakes. Her laugh is infectious, and Sam laughs with her. Sam looks ten years younger. He has renewed energy and motivation for Hunting. Castiel realizes Sam looks like he's enjoying life for the first time, and Castiel hopes Eileen knows how much of a difference she's making.
Tomorrow, Sam and Eileen are going to Ireland. The trip is a bit spontaneous, and Dean didn't like the idea at first, but even Castiel felt weak after seeing the pleading look on Sam's face. Dean couldn't resist, and he was never really opposed in the first place. He's just worried. As always.
Speaking of Dean… He is happy too. Dean and Heather keep stealing fries from each other's plates, and there's a bright spark in Dean's eyes Castiel has never seen last for more than a few seconds, but Heather has somehow managed to keep that light there. Dean looks beautiful. And Castiel allows himself to stare. He's leaving after this, and he wants to commit every detail of this night to memory.
He doesn't want to forget the way Sam always insists on getting salads but allows Eileen to feed him her fries. Or the way Dean makes a joke and waits for everyone's reactions.
Castiel doesn't want to forget how diners are. The muffled conversations enveloping them. The smell of greasy food filling the air. The sticky chairs and cracked tables. The imperfections of Earth are what make it truly beautiful. Castiel will miss it terribly. He has to keep reminding himself he's doing what's right by leaving.
They finish eating all too soon and make their way back to the parking lot. The autumn air is cool, and the Hunters all put on their jackets. Eileen stole one from Sam, and she looks ridiculous—but adorable—since Sam's jacket all but swallows her. Sam is staring at her with a small, brilliant smile. His eyes are so warm and fond. Dean smiles at Castiel before following Heather as they walk towards the Impala. Castiel looks up at the stars. Even the stars look different in Heaven than they do here. He stops and stares.
"You okay, Cas?"
Castiel looks back down.
Heather, Sam, and Eileen are piling into the Impala, but Dean is standing in front of him, watching him.
Castiel smiles. He forces down the sad yearning bubbling up inside his chest.
The yearning he is familiar with. Especially when it comes to Dean. But he knows his sadness is him already mourning the loss of his time on Earth.
Castiel finally answers, "Yes, Dean. I was just admiring the stars."
Dean looks up. "They are bright tonight."
Castiel stares at Dean. The Hunter is looking up at the sky, and the stars reflect in his eyes. Castiel says, "Yes."
Dean meets his gaze. "You sure you're okay? You've been quiet tonight."
Castiel smiles again. "Yes, I'm sure."
Dean gives him a small grin in return. "Good. Just makin' sure you remember you can tell me anything, okay?"
"Of course, Dean."
Dean studies Castiel for a moment, flicking his gaze over Castiel's face as if he's searching for something. Dean can always tell when Castiel is keeping something from him, but he doesn't press any further. Dean nods at his car. "We're doing movie night. You comin'?"
Castiel wants nothing more than say yes. But he can't. Tonight he is going to drive to Heaven's gate. He can't put this off any more. Castiel's eyes drift towards his truck then back to Dean. "Thank you for the invitation, but I think I'll take a drive tonight instead."
Dean licks his lips and nods. "Yeah, okay." But he studies Castiel again like he did before.
"I'm fine, Dean," Castiel reassures.
"You sure?"
Castiel raises his eyebrows and grins in amusement. "Yes, Dean."
Dean swallows but nods. "Alright, Cas. See you soon."
Castiel hopes he doesn't see Dean soon. Because that would mean Dean is in Heaven. And Dean would be dead. "See you later, Dean."
Dean reaches out and squeezes Castiel's shoulder before turning around. Castiel watches him walk away before realizing he's about to cry. He quickly turns towards his truck, fishing his keys out of his pocket. He gets inside his truck and hears the Impala roar to life. He watches her pull out of the parking lot and speed down the street, her red tail-lights glowing like watchful eyes.
Castiel stares at the lights until they disappear. He takes a deep breath, steeling himself. You're making the right decision, he reassures himself. He starts his truck and drives away in the opposite direction of Dean. The second Castiel leaves the parking lot, he cries.