A long time ago they stopped lying to each other. Sam is really doing his best to be honest with Dean and himself. The trouble is not cutting off Dean only because he hears exactly what he's pushed out of his head thus far. Dean is right. It slowly starts to sink in when his brother says it.

Sam shakes his head the whole time.

It's how Dean drops the big gesture thing right at the end when he stops. His wheels never stopped spinning but he never considered before now how maybe there is something Jack could do. He twists and turns his head to weigh how desperate he is vs how much he didn't want to get other people involved. He found that the shame was poor company for actually being able to reach Ruby, and accepted the idea with an outward nod.

"I know you mean well, Dean, in pointing out-- I think I need to take whatever options there are left and talk to Jack. I can't leave it like this. I won't. I don't care if I'm not supposed to write letters or look for another way. If Heaven is supposed to be where we find peace, I haven't felt it in..." He can't finish that sentence because honestly he can't pinpoint when his uneasiness set in. Maybe it was there from the start. "I really can't move on." He adds.