⬆️ This is not the reaction of someone who wants to hear "You're our brother."
You can literally see him thinking about where this conversation might be going as Dean opens up to him.
Look at that huge swallow as he tries to work out how to respond to that.
Look how many times his mouth choses words without saying anything before settling on 'thank you'.
Look at him shift uncomfortably, grasping at more things he wanted to say as the phone rudely interrupts him; then curse it out silently as he tries to hide his disappointment.
Look at him staring out into nothing... Cas had more words he wanted to say. Things he didn't get to tell Dean.
This is Cas' version of the 'purgatory confession' cut short.
Bonus: WTF EVEN IS THIS LOOK?! The longing! The yearning! WTAF. That angel is in love.
