Oh, I definitely agree that Sam is taking everything in the worst light because he's so depressed. I'm just not quite sure why Sam is so down to begin with -- I don't get what makes 'this' the final straw, or what 'this' even is -- Jack disappearing? Kaia dying in front of them? How was that worse than Mary disappearing and Cas dying in front of them?

(I do think it plays better if one has read Sam as barely hanging on to optimism/sanity for months/years now, and his grip finally just slipped. But even for most of this season before this ep, there were few hints that anything was really bothering Sam. I'd have liked to have gotten more all along -- even if I'm very happy to be getting something concrete now!)