I am usually awed by your analysis, manhattangirl, so it's refreshing that I don't agree with you regarding Ennis having abandonment issues. I think he kept Jack at a distance because he didn't know how to handle this thing with no name, with no reins on it. I see Ennis as someone who likes his world very organized and neat. With everything in its place, and this thing with Jack just couldn't fit into his world. Once he learned it is love, with Cassie showing the way, he was ready to jump in with both feet, sending the card to Jack. And when it fell apart, he pursued Jack all the way to Lightning Flat, which he could have done, but never did when Jack goes to visit his folks. I felt that Jack was inviting Ennis to come along for a couple days, and probably had done so explicitly before, but was rebuffed.
Ennis was simply not ready. It took a lot to change his thinking. Cassie, the shirts, the realization that Jack's Ma accepted them all along... I watched that kitchen scene again, and this time I didn't cry because I was just so transfixed by the non-verbal communication between Ennis and Jack's Ma. I still cried when Ennis found the shirts, but that's about all. I think I've got my PBS out of the system for now, until the next time when emotions overwhelm understanding.
I agree with you, however, that Ennis and Jack as a couple will not always be smooth sailing, as when they lived their fantasy of Brokeback Mountain. Real life can be difficult on couples. How they deal with problems can be seen from their shooting an elk for food, Jack taking care of Ennis when the bear spooked the horses, and the two worked together to get the sheep back after the storm. I think they will make a good team, provided Ennis can rise above the wall, the fortress that he built. With Jack's Ma helping, I think the two of them has a good chance making it on the ranch, in spite of the old man. Perhaps, because of the old man, since having a common enemy is the best way for them to bond.
I agree with your observation that Jack may not know Ennis' love for him. His back was turned when Ennis broke down at his words, You have no idea how bad it gets. I think he has no idea that Ennis suffers also. Then again, perhaps it's his new stud duck persona that is now ignoring the very thing that he saw and loved in Ennis back in '63, that Ennis was the personification of loneliness. He does not enjoy it, just stand it because unlike Jack, he doesn't know how to fix it. Once he realized he doesn't have to be alone, he became alive. His footsteps coming down those stairs and across the kitchen floor were lighter, lightest in the whole movie. I always wondered why these cowboys drag their feet. Now I realize it is the genius of Ang Lee, preparing the moment when Ennis is presented as the new man, light on his feet, with love in his heart.
Both Jack and Ennis changed during the movie, in the twenty years, as expected with anyone, but they changed in different ways, and at different speed. Jack is quite right that he is not Ennis. If he truly loved Ennis, he would have found a way to deal with it. He tried his hardest, but as he said, Ennis was too much for him, just as he was too much for Ennis at the end, asking for more frequent meetings, instead of coming right out and offered to build a cabin in his parents' ranch. I think Ennis would have been ready for that, instead of just two guys living together. Anyway, I'm beginning to ramble off topic.

I personally believed Ennis would never live with Jack. This is someone with deep abandonment issues, keeping Jack at a distance where he could handle him emotionally was all Ennis could cope with.
Remember how his reaction when they parted that first summer. So devastating, his pain so deep, that it was a physical reaction losing someone he'd grown emotionally, mentally, and sexually attach to.
How would've been if they did live together? Would Ennis smother Jack with his fears, would Jack feel the pressure of constant reassurances that he wasn't going anywhere?
We got a hint of the bickering that goes on between them, when they argued when Jack suggested Ennis moved to Texas. Ennis could be pretty nasty and hurtful towards Jack, but protective of him at other times. We also have the issues of Jack's little trips to Mexico, and Ennis's reaction to them, how much would the knowledge that Jack could do this play into Ennis's mind.
I'm not looking at Ennis being gay, straight or whatever, but a man with problems that started in childhood, carried with him to adulthood, and how it shape and moulded him as a lover, a companion to another human being for life. Would Jack take the time and understand this of man he loved so much.
"I not you, Ennis", that said a lot. Could Jack and Ennis really survive as a couple living together?