Castiel…
His name still lingers upon his tongue, and Dean can taste the guilt that burns inside his mouth. Burning so deep, Dean feels as though his soul is bleeding from this scorching heat, and the plain torture his name now brings. But Dean knows his souls not bleeding; however he is certain it's in fact shattered, like his heart.
"Without your powers, you're basically just a baby in a trench coat."
Dean will never forget the reaction of the angel, the way he looked away, stroppy, like a little child. It always used to make Dean smile. But not now, the sheer thought of smiling seemed painful. More than once though, Castiel reminded him of a child, like the many times when the angel was so confused and innocent, but Castiel was always a baby in a trench coat to him. He was the newest member of Dean's family, like a new-born would be, Castiel was introduced to them a blank slate, Dean carved and moulded him, introducing him to free-will. Now he's lost him, lost without him. Ultimately Dean blames himself, and why shouldn't he? Everything else seems to be his fault.
"His name's Castiel, he wears a trench coat."
And it's that very trench coat that Dean pulls closer to his chest, allowing the mix of his sweet angel's scent and pond water to fill his nostrils. He shuts his eyes, weak from the lack of sleep and lack of a proper diet, and allows the smells to overpower him. Dean feels the tears that threaten to fall, and just lets them fall.
"I'm sorry, Dean."
The last time Dean truly saw Castiel, he was overly apologetic and Dean regrets, strongly, not giving the angel the right response. "It's okay, we'll make it through, we always do" or even a pat on the shoulder, something. Anything. That's all he wanted, and he didn't get it. Yes, he betrayed Dean, but Dean should have forgiven him, he was like a brother to him after all. But Dean didn't forgive him, and now there's an ever heavier weight on his shoulders, a painful reminder of everything Dean's done wrong. Now all Dean can see whenever he shuts his eyes is the fragile, defeated angel he last saw. It was evident that Castiel had now given up on everything, everything but Dean. In his last moments, knowing he couldn't fight back the Leviathans any longer, he yelled at Dean to run. He was looking out for Dean until the very end, he won't ever forget that.
"Castiel," he whispers softly, the name scorching his tongue again, "I'm sorry too."
Despite his words falling on deaf ears, he feels better; his shoulders not as heavy. Dean begins to feel sleep overcome him and hugs the trench coat tighter, not caring that it was still damp. He lets his head fall against the soft material, feeling the slight wetness tingle his cheek, and falls into a deep sleep. The trench coat is now Dean's second skin, forever on him. He can't sleep without it, psychically, or nightmares and memories haunt his mind. He regrets never hugging his angel, every second of every day, and this is the closest he'll ever get to doing so.