Jack had given up on Ennis. The 1983 campfire scene was their farewell as far as Jack was concerned. That to me is the explanation of his memory of the "dozy embrace" and his looks during that memories aftermath, Jack was remembering those wonderful days on the mountain in their youth, and how it was all gone, all irretrievable.
Jack was going to try to bring Randall north to the Twist ranch, otherwise he wouldn't have told OMT about his plans.
Ennis after his conversation with OMT finally fully realizes 3 things:
1) Jack really loved him
2) He really loved Jack
3) Jack was planning to leave him
this is why the Twist ranch closet scene is so deeply emotional, all of the regrets, the shame, the loss, the loneliness of their lives cascade down on Ennis at the same time. That is why I continue to feel in that moment Ennis had a transformational epiphany, he finally connected with his true nature. Too late for Jack, and that is to me the heart of the tragedy of the Brokeback story.