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thread of dean openly expressing vulnerability around cas because he's one of the (very) few ppl that won't judge dean for it 
> 4.03 | in the beginning
> 4.16 | on the head of a pin
> 4.16 | on the head of a pin
> 5.03 | free to be you and me
> 5.17 | 99 problems
> 5.14 | my bloody valentine
> 6.20 | the man who would be king
> 5.20 | the man who would be king
5.22 | the man who knew too much
5.17 | the born again identity | this scene is something so personal to me
> 7.02 | what's up, tiger mommy? | iconic
> 7.02 | what's up, tiger mommy? | this scene is my religion
> 8.07 | a little slice of kevin
> 8.17 | goodbye, stranger | this is the most prime example i think
> 9.03 | i'm no angel
> 9.10 | road trip | notice how cas didn't tell him to "man up" or "suck it up"? he reassured him and calmed him down.
> 9.10 | road trip | dean went from fretting and on the brink of tears to calmed and smiling. such an underrated scene.
10.09 | the things we left behind | any other person would've just accepted the "im fine"
> 14.14 | ouroboros | cas always gets him to open up
> 15.09 | the trap | absolutely legendary
end of thread 
there're many more instances but im tired
there're many more instances but im tired
in conclusion: dean has a hard time opening up to people because he was raised to always be "tough" and was taught to repress his emotions, put his brother's wellbeing before himself always. as a result of this, it went beyond just putting sam first to everyone else too
he doesn't show vulnerability to anyone like he does castiel, not even sam, because he thinks that he's built this image of himself in sam's head; the big brother who is always fine. he doesn't want to sully that.
