The nightmares continue to haunt Dean, and almost every night Cas wakes up knowing he is needed. It makes Cas feel less useless to see the fear gradually disappear from Dean's hazel eyes as he talks with the ex-angel.
Things are going well, until they face a demon.
It is the first demon they have come across since the Apocalypse and they are slightly rusty, especially Castiel, who still doesn't really know how and when to defend himself in this weak human body. He breaks his arm.
Cas himself is fine, once he has overcome the pain, and they are soon back at the motel. But Dean is shaken up. Ever since nearly losing Sam to Lucifer, he has become even more protective of those he cares for, and he seems to realise with a shock that Cas, too, is now fragile.
Combined with the demon, this realisation gives Dean the worst nightmare he has had for a while. Cas knows there is something different as soon as he wakes up and sees Dean.
"Cas..." Dean croaks.
Cas instinctively moves to stand next to him and touches his shoulder lightly. "Dean, whatever you saw, you know it isn't real. You're safe, you're with me and Sam."
Dean nods and swallows thickly, but Cas can tell he is still shaken. He gently puts his arms around the hunter, and though he has to twist around awkwardly, he feels Dean relax into the hug and decides it's worth it.
They stay like that for a while, and it dawns on Cas that at some point, Dean has fallen asleep. He starts disentangling himself to return to his own bed, but Dean's arms tighten unconsciously so that Cas is effectively trapped.
Cas freezes, unsure whether to wake Dean up, or try and shuffle out of the firm embrace, or...
He catches sight of Dean's face, and it makes him decide immediately. Dark bags have settled heavily beneath the hunter's eyes, but his expression at the moment is calm, almost childlike in its innocence, and Cas cannot bear to disturb his peaceful sleep.
Slowly, he insinuates the two of them underneath the duvet into a more comfortable position, and then he too gradually drifts towards sleep.