It feels like a red-hot punch in the gut. Of course, Dean doesn't show it. He's still smarting (physically and emotionally) from the vicious attack of the Leviathan. It was all the more harsh coming from the nerd angel he calls- called a friend. It doesn't seem real. Even as he picks up Castiel's sodden trench coat, even as they walk away from the water supply, it still hasn't sunk in. Yes, Castiel could be a manipulative son of a bitch at times, and his social skills were borderline non-existent, but he was the one who saved Dean. At times, Dean wished he hadn't been brought back. The memories of hell he held twisted themselves into darker thoughts, which grew and grew. But that wasn't the point. Someone still helped. Castiel still helped him back. The sight of Castiel torn apart from the inside by Leviathan was horrific. The sheer power of Leviathan to be able to take apart what guns and explosions didn't would linger in both his, Sam's and Bobby's memories. Dean left the trench coat in the back seat of the Impala, almost if only to have the sense of something in the back of the car that wasn't a weapon; a small reminder of the angel that saved him.