It didn't register at first. Not for days. His own thoughts were too loud; he couldn't have heard anything else anyway. It wasn't until the silence settled in around him and Lisa looked right at him and said something, repeated it when he frowned in confusion, when he said "I can't hear you" and tapped his right ear once and followed it unconsciously with the sign for closed that he realized.
Ear closed. Deaf.
Ben stared. Lisa cried. Dean didn't know whether to cry or to curse Cas' healing abilities. That lasted until Cas turned up in a dream and apologized for not being able to do more than lend Dean his own ears until he got to Lisa; the physical damage had healed with everything else, but the nerve damage wasn't something Cas knew how to undo. Dean woke up shaking and crying, and Lisa held him until he cried himself to sleep.
But that was May. Over the summer, Ben and Lisa eagerly learned ASL, and Dean got better at lip-reading and found a job at a garage where his deafness wouldn't put him in danger. That obstacle, as much as Lisa's support, has given Dean the motivation to keep going, not to let the grief over Sam's death cripple him, not to give in to despair. If he can learn to live without his ears, he can—eventually—learn to live without Sam.
Oh, I've seen fire and I've seen rain,
I've seen sunny days that I thought would never end,
I've seen lonely times when I could not find a friend,
But I always thought that I'd see you again.
Neither is easy, though, and tonight, sitting out here on his tailgate with a bucket of candy, dressed up like his best friend (though most people guess Columbo, he can see, and he doesn't bother to correct them) and watching the neighborhood wander by... it hurts. All of it. He's wearing Cas' coat and Sammy's tie and a belt he'd borrowed from Bobby eons ago and forgot to give back, and none of them are here to laugh at him, and he couldn't hear them even if they did. Just like he can't hear the laughter and the funny voices and the childish "Trick-or-treat!" that he knows are echoing all around him.
He's even begun to forget what their voices sounded like, Mom and Dad and Sam and Bobby and Cas and Ellen and Jo and Ash and...
... everybody he's gotten killed.
(Here come more trick-or-treaters who don't know he can't hear. Quit being so maudlin, Dean. Dude. Maudlin? Shut up, Sam.
He'll never forget Sammy's laugh.)
Well, he can get Bobby on video chat later, probably. And maybe Cas'll stop by in a dream again. No, he totally did not just pray that. But Sam... Dean can't just drive down to Palo Alto anymore.
Sleepless hours and dreamless nights and far aways,
Ooh, wishing you were here...
He tries to put his old favorites on his mental jukebox to chase the quiet and the memories away. And it works for a while, until the evening winds down and Ben and Lisa come home—Ben dressed as a wendigo, Lisa as Kali, and no, he is notgoing to play Gabriel tonight; that was one thing he never needed to know about their favorite archangel.
But the lights are going out all over the street, and Dean's brain picks the last track of the evening's playlist without his consent:
Hello, darkness, my old friend,
I've come to talk with you again...
Lisa signs for him to come inside, and he does, because he can't face the darkness and the silence alone. She's good for him, his Lisa. But Bobby's not online, and Cas doesn't show up, and all night Dean's dreams are filled with the sounds that Sammy has to live with for all eternity.
Fire and Rain - James Taylor
Wishing You Were Here - Chicago (with backing vocals by the Beach Boys)
The Sounds of Silence - Simon and Garfunkel