See that? See how Cas isn’t looking Dean in the eye? It’s because he can’t. Try listening to the man you rebelled for, fell for, died many times over for, call out to you every single night. Try listening for his cries for help and pleas to know if you’re even alive or if he’s truly all alone. Try using every last ounce of self control you have not to return to his side and tell him that you never left him, that you were there protecting him all along. Try risking him hating you just so he’ll leave you behind and have an actual shot at getting out. Try doing all of that, and then tell me if you’d be able to look him in the eye when you tell him, “I know.”
S8E23 “Sacrifice”: Do you mean do I think they’ll kill me? Yeah, they might.
This scene shows just complete emotional vulnerability between Dean and Cas. Here is another time when Dean encourages Cas to talk to him about whats going on - he wants to know how Cas is feeling. He knows what closing heavens gates could mean. So does Cas; he knows that they could possibly kill him and he is willing to admit this to Dean and talk to him about it. Both Dean and Cas have never really been able to be vulnerable to anyone else - but here they are completely susceptible to each other.