A/N: He also learns his actions might be a little creepy, but this information comes to him as too little, too late.
The first time he does it, it's not entirely intentional.
The muffled, painful moans that he hears coming from Dean are...well, honestly, he finds them irritating. He came to watch over this frustratingly mortal being and make sure he was safe, not listen to his aggravating inability to sleep.
Unthinkingly, he places his palm to Dean's shoulder, allowing himself into Dean's dream.
He finds it filled with hellfire and tortured souls.
Had he not already saved Dean from this fate?
Why is he reliving it in in his subconscious?
Are mortals so frail that they cannot alter their own thoughts while asleep?
He sighs wearily before making it all disappear, letting the scene fade out. He reaches into the depths of Dean's thoughts and memories, finds a peaceful moment and tugs it forward, letting it replace what had been.
A lake, a slightly rugged chair, and fishing gear appear. Dean sighs contentedly into his pillow.
Castiel lets go of his shoulder and relaxes.
It's quiet now.
XXX
The second time he does it, he thinks he's being helpful.
Dean's thrashing in his sheets as he desperately and repeatedly calls Sam's name, begging him not to let Lucifer take him.
Sam, Castiel notes, is safe, sound asleep, and snoring on the other side of their motel room.
It would be foolish, he thinks, to allow Dean to continue to be in anguish over a hypothetical situation, a situation that may never come to pass.
He grips Dean's wrist and projects the image of Sam's sleeping form until it saturates over all of Dean's fears and concerns and stops the nightmare.
He then brushes Dean's hair back from his forehead.
He isn't sure why he does this. He just feels a very strong and very unangelic wave of affection for Dean.
He senses, almost immediately, though, that, everything he just did was wrong.
He's becoming far too attached to his charge. He's allowing himself to believe that there is an alternative to the civil war that his brothers have been planning.
He's...he's falling.
He unfurls his wings and directs himself home.
XXX
In the weeks following, though, the same thing happens, in much the same way, several times more.
XXX
He suspects, after the apocalypse has been averted and he has brought Sam back from hell, that Dean will no longer have such horrifying dreams. So, he returns to Heaven, where he believes he's needed.
And he stays there, his energy focused on stopping the angels from having a different civil war - a plan, that is, by and large, failing.
He stays until Dean calls out to him, by name, in his sleep.
He knows that he shouldn't leave the other angels, as they are looking to him for leadership, but Dean needs him too.
Or so he thinks.
When he arrives, a girl, Lisa, is pulling Dean closer, tucking his chin against her collarbone, rubbing her hand over his back, telling him it will be okay.
As she does, a strange, uncomfortably human feeling, washes over him. He isn't sure what the feeling is, but it makes him put his hand back against Dean's shoulder and look in. He sees, briefly, that Dean's now dreaming about listening to rock music in the garage while Ben and Lisa dance goofily in the background. They're all laughing and smiling.
A wistful feeling overtakes him, and he decides that his help is not needed here after all.
He leans against Lisa's ear and whispers softly, "Take care of him. Please."
XXX
In the months following, as Dean begins to call for him more and more frequently, Castiel wants, desperately wants , to go to him, but he knows that it is ill advised. He is keeping secrets from Dean, and the weight of it is growing on him.
Yet, in a moment of weakness, he goes anyway.
He discovers something troubling.
Dean is dreaming about him.
But...
But...
It changes nothing.
XXX
Angels do not dream, so Castiel does not dream.
In his waking hours, in the psych ward, he bears witness to Sam Winchester's hallucinations and tries desperately not to remember what he has done to Heaven.
And when he sleeps at night, he is thankful for what he is, for he could not bear to dream.
XXX
Every night, in Purgatory, it's the same.
Dean prays to him, trying desperately to find him, saying things like, "Look, Cas, if you're close, you should see this tree. Come on, man. You got to be close. I know you gotta be. Yell for me, if you're hurt or something. I'll patch you up, get you out of here. Promise."
And every night, Cas winces and keeps going. He needs to be here. He needs to do penance. And Dean...Dean needs to go home.
He knows that if Dean finds him, Dean will only suffer.
Yet, knowing this does nothing to quell the ache in his heart when Dean cries out to him again, after he's fallen asleep, as his nightmares seem to, overwhelmingly, involve him.
He longs to go to him, to reassure Dean that he is safe, but Dean is safer without him. Dean is better off without him.
He tells this to himself, over and over.
XXX
When Dean does finally find him, Castiel truly wishes that he hadn't.
But he decides that as long as he is with Dean, he can still soothe away his nightmares.
Yet, strangely, despite being in grave danger, Dean seems to, mostly, be at peace when he and Benny watch over him at night.
He mentions this, offhandedly, to Benny, who gives him a pitying look. "This has got nothing to do with me, brother. But I think you know that."
He wishes he didn't.
XXX
"I'll watch over you."
"Yeah, that's not happening," Dean says, and Cas is mystified. He's been watching over Dean for years now. Did Dean really not want him to?
It was a thought that had never occurred to him before.
He mulls over this as he picks through Dean's belongings. He wonders if, perhaps, he should stop interfering with Dean's dreams.
XXX
Likely, he discovers, months later, Naomi would have stopped him anyway.
XXX
When he has his first nightmare, after Metatron cuts out his grace, the first thing he thinks when he wakes up, in a cold sweat, lying in the grass across from a bus stop, is that Dean could make this better.
He sits up, rests his chin in his hands, and wonders, if Dean was not allowing him to stay in the bunker, was he also not allowed to contact him?
He draws his cell phone out of his pocket and holds it against trembling fingers, willing himself to dial Dean's number. The dark outlines of his fallen brothers and sisters' wings remains etched in his mind, even when he closes his eyes and tries to picture something else.
He looks a Dean's name in his contact list, holds his finger over the button, and finds that he can't press it.
He isn't sure why Dean told him to leave, and he's not certain he should admit to suffering so much human weakness.
So instead, he tries to imagine Dean pressing his hand to his shoulder, whispering to him softly that it's okay.
It helps enough that he tries to imagine it every time afterwards, even when the nightmares are about Dean, as, he finds, they often are.
XXX
"Nora!" Cas cries out as ten angels blast into the Gas N' Sip. He puts himself between her and them, but, without his powers, he feels, well, powerless. He reaches for one of the lighters on the cash register display, but his brothers only laugh before rendering the tool completely useless and blasting Nora back against the dairy case. "You abandoned us, Castiel, for this place?"
He thrashes on the sheets, and Dean's hand comes to rest on his shoulder. "Whoa, whoa, Cas, calm down. You got to wake up. You're going to fall off the bed, and that's going to do nothing good for that wrist."
"Dean?" he asks. He sits up, and he feels dizzy. Bits and pieces of earlier filter in. His wrist is throbbing.
"You okay?" Dean asks. He shakes his head before leaning into Dean's shoulder, resting against the crook of Dean's neck. Dean puts a hand against his back and rubs at it. "Well, you will be. Okay?"
He's not sure Dean's right, but this... this helps.
He nods. "Alright."
XXX
The stolen grace does not restore his wings, and he finds that, though he can hear Dean's cries into the night once more, in unconscious prayer, he can no longer fly to him, whether Dean wanted him to or not.
He settles, instead, for texting Dean whenever it happens. He sends mundane comments on the plants and animals he sees on the road. He adds smileys and other emojis. Sometimes, he takes pictures of his car and asks Dean to explain it to him.
Usually, whether Dean replies to him or not, Dean's unconscious distress signal stops afterwards, and he thinks that this is helping.
But, as Dean's volume of nightmares seems to, inexplicably, rise he hopes that it's enough.
He suspects, though, that something is deeply wrong.
XXX
When Dean's nightmares stop entirely, because he no longer dreams, Cas wishes for a comfort neither of them can have.
XXX
When he is back to being not quite an angel, and Dean is back to being, mostly human, it's as it was nearly a year before.
The volume and intensity of Dean's nightmares increases steadily over time, as the Mark takes over, and Castiel fears more and more what is to come.
XXX
The night after Dean kills Cain, his screams echo hollowly against the bunker's walls, and Castiel goes to him without a thought.
He stands above Dean and rubs at his shoulder until Dean looks up at him, bleary eyed. "What are you doing, Cas?"
"Watching over you," Cas says simply. And he thinks Dean's going to balk and bristle, uncomfortable with the invasion of personal space or privacy, or whatever it is that he's violating, but Dean merely squeezes his shoulder in thanks.
Then, unexpectedly, Dean looks up at him, his expression unusually shy, before gesturing awkwardly to the free half of his bed, "If you're, uh, planning on playing Mr. Sandman anyway, there's, you know, space..."
He ducks his head sheepishly, and Cas raises an eye before easily clambering in.
XXX
The past, and sometimes the new present, will always haunt Dean and Castiel. They both know this far better than they would like.
Yet, after Castiel becomes human again, and the Mark is gone, the two of them, more often than not, find comfort and reassurance, in the dead of night, in the other's arms.