When Cas turned human, Dean didn’t expect him to start dying. He didn’t know what he expected, if he was honest. Thought that all those falls, scrapes, all those knives and nails stabbed into him, those bullets shot into him, would just..not exist. That they would be magically healed and everything would be fine, would be normal.
He was wrong.
It starts off with Cas being completely immobile. Stuck in bed, his head throbbing, eyes barely able to open. He can’t even speak, his throat working and coaxing and trying to push a voice out. To put a shape to vowels. None come.
His health decreases as the week goes on, and soon Dean refuses to leave the motel. Hangs a ‘do not disturb’ sign on the handle, and locks everyone else out. The shades are drawn, and the only source of light is the lamp on the bedside table.
Sam calls frequently, but Dean lets his phone die.
Cas doesn’t start coughing blood until halfway into the second week, his body convulsing and shaking, blood splashing against the pillows and sheets, staining everything it hits. It’s everywhere, a few drops landing on Dean’s face even.
Dean carries him to the bathroom, undresses first Cas and then himself. He turns the water on hot, then cradles Cas in his lap in the tub, water spraying over them. Cas can’t open his eyes at all now, the effort of it taking too much energy. The coughing fit has left him sagged against Dean’s chest, breathes scratching and scraping out of him in soft wheezes.
Dean runs his fingers through Cas’ hair, sings Hey Jude softly to him.
When the second week comes to an end, and Dean is lying in bed with Cas tucked into his side, Dr. Sexy M.D. playing quietly, that’s when Cas finally passes away. One minute Dean can feel the soft puffs of breath on his neck, the slight rise and fall of Cas’ body, and then it slows until he doesn’t feel anything anymore.
He knew it was coming, of course. Knew that Cas dying was inevitable. But that doesn’t stop the ache, the pain. The never ending flow of tears as they soak into Cas’ hair, doesn’t stop Dean from shaking his angel’s lifeless body and begging please.
Eventually Sam tracks them down, breaks into the room. He almost thinks Dean is dead also, with how still he’s lying next to Cas. But then he can see the rise and fall of his chest.
They burn Cas’ vessel, and for the first time in years Dean says a quiet prayer.