Right, they're both regressing, though neither of them would call it that and though if anyone ever had a reason it would be Sam. I think they can get back to choosing to rely on and be reliable for each other, but they've got a way to go.

I don't think we disagree about letting the kid live: it was boneheaded (for anyone who wants to live a long and healthy life) and there was no way Dean would kill him. Dean can't kill kids and this way he gets a chance to be justly slaughtered--how could he resist a twofold reaffirmation of who he is?

I think Sam relates very easily to many people and can be very perceptive, including being perceptive about the fact of Dean's death wish, but he and Dean have collaborated on a family structure in which Sam doesn't always get why Dean is acting the way he is. Also, I am giving Sam a big Hell pass on noticing how far Dean's falling; he did slightly better when he just had psychic powers and the demon that killed his mom and Jessica was after him, but, in retrospect, he had it pretty easy then.