A fleeting image in episode 8x07 which tells so much more than we think.
This is Dean's expression when Castiel tell him: ''You can't save everyone my friend. Though you try''.
I saw that, I actually noticed it the first time I watched it! I was so overcome but that expression, because it meant that Cas had managed what the others had failed to do. He went straight through Dean’s disillusioned defences, broke the gates of his torment and actually realised the true nature of Dean Winchester.
He unravelled Dean in a way that on one else could. And Dean could not believe it, because all this time he thought that Cas absolutely hated him. Blamed him for his death, for ”letting go”, where Cas explained that not only did he not blame him, but actually felt proud and touched by Dean’s trait to save the others.