Silence was a strange thing to grow acquainted to and then miss. Though, Dean supposed it wasn't so much silence itself as the feeling of Castiel slotting silently into the space near him. Almost always with no regard for personal space, appearing right on the border of Dean's sense of self. As if somehow to transport himself near, Castiel used Dean's soul as a beacon for his Grace to come ashore to the right harbor.
For the last few weeks, Castiel had been a fairly constant fixture in his and Sam's less than regular lives. There was traveling back in time, and it was always a sucker punch to see his mom. Feelings flooding inside him with parts more bitter than sweet but irrevocably needed. Then the ridiculous fat cupid, which had led to the acquisition of a third ring but the unsettling realization that Cas could fall victim to the call of the horsemen. Only to show even more human vulnerability as his face contorts, trying to wrap around Joshua's message and unsure of what to do. To him lurching quite literally back into their lives, emptied and despairing. When Cas brokenly proclaims that he is a poor example of an angel, it is such an echo of Dean's own self-loathing that his hands clench in sympathy and frustration at not being able to do anything. But what could he do anyways? He's always been poor at comfort, and he shelters emotions deep into the back of his brain to not be awoken. Solace is not a tune that Dean has ever felt comfortable playing along to and a role he never welcomes.
And that ability to hide away his guilt comes into use when he decides that he absolutely must go save Adam. And to do so, he takes skills taught to him by someone who has never intentionally harmed him to draw a banishing sigil against Castiel. So when Castiel finds him in the town and flattens him to the ground with righteous fury, singing with all of his angelic might, Dean only finds it just. But when Castiel volunteers to get them past the five angels in front of the Green Room, Dean can only humbly nod and accept the help.
So when they haven't heard a single peep from Cas and his phone only rings out, Dean can't help the quiet upset that blankets his insides. He keeps looking around him, habits trained by long years of a Hunter's wariness. Instead of just alertness, his glances are tinged with concern, anxiety, and a tugging of his soul that he is not quite sure that he is ready to admit to himself. He wakes in the middle of the night, wrenching from unsettling dreams that he can't quite recall that hover at the edge of his mind. And his first instinct is to cast his gaze around the room for a familiar trenchcoat so he can lock eyes with bright blue and feel the relief flooding through his system.
So when Castiel finally calls him, he can barely choke back the tide of emotion rising in his chest. Especially when he finds out that Castiel has been hurt these last few weeks, and he was completely unable to do anything to help the angel. What comes out of his mouth is an angry "You want to elaborate?" which was not what he had meant at all. And when Cas shows up while they're fighting Pestilence, he can't help the joy that he feels as he whispers his name.
Dean waits until it's a moment when the two of them are alone to clap an arm around Cas. He just smiles at Cas, trying to show him the comfort that he feels. Castiel shares his gaze for a moment, question apparent in his eyes but leaning gently into Dean's embrace. Dean can't help it that in response, his other arm wraps around and that his head rests on Cas' shoulder for a brief second. His whole body sighs in relief, and he whispers, "It's good to have you back, Cas." And Cas replies, "I could never really leave." And Cas' words are a validation and a promise that ring in Dean's ears long after their embrace has ended.