I love it when Sam’s little brother tendencies just come out. Like, he is so serious most of the time, but on some occasions when he is with Dean, he just reverts to being an annoying little brother.
I remember Jared saying at a convention once that when one brother is down the other one is there to lift him up despite feeling the same because if they both fall apart at the same time there would be no way back up. I think we’ve seen a lot of that this season. That’s why I love this scene. Sam needing reassurance and Dean willing to talk things out.