As to Jack's death, I think it was really an accident and nothing more. The SS narrative establishes that Jack's death was accidental:
Ennis didn't know about the accident for months until his postcard to Jack saying that November still looked like the first chance came back stamped DECEASED.
But Ennis's reaction upon hearing Lureen's account of the accident is that Jack was murdered:
No, he thought, they got him with the tire iron.
Yet he's not sure:
The huge sadness of the northern plains rolled down on him. He didn't know which way it was, the tire iron or a real accident, blood choking down Jack's throat and nobody to turn him over. Under the wind drone he heard steel slamming off bone, the hollow chatter of a settling tire rim.
Later, when Ennis learns from Jack's father that Jack had talked (right after the spring 1983 confrontation) about divorcing Lureen and moving back to the Lightning Flat ranch with a ranch neighbor from Texas, Ennis is convinced that Jack was murdered:
So now he knew it had been the tire iron.
Regarding the flash in the film of Jack being beaten, that was not a news flash. According to the 2004 screenplay and Ang Lee's comments in an interview with Charlie Rose, it was just what flashed through Ennis's mind at the time.
The murder is only a prodct of Ennis phantasy that has to do woth childhood experience -remember the scene when he was a boy at his father's hand and had to see the gay farmer couple that was killed."There was these two old guys ranched together down home, Earl and Rich—Dad would pass a remark when he seen them. They was a joke even though they was pretty tough old birds. I was what, nine years old, and they found Earl dead in a irrigation ditch. They’d took a tire iron to him...Dad made sure I seen it. Took me to see it. Me and K.E. Dad laughed about it. Hell, for all I know he done the job."
We don't know what happened to Rich.
Laureen on the phone reacts and sounds a little bit strange because she knows or at least feel the rivalry about Jack's love......Actress Anne Hathaway put a spin on Lureen's lines that made it sound like while speaking with Ennis she suddenly realized he and Jack were lovers.
I found that interpretation implausible. How could Lureen believe Jack was in love with a man he saw only one or twice a year on brief fishing or hunting trips 1200 miles from Childress? If would be more plausible for her to believe that they were simply old friends.
Lureen didn't know (or suspect) anything more than what she said she knew:
“Jack used to mention you,” she said. “You’re the fishing buddy or the hunting buddy, I know that."
The old bastard Twist wants to humilate Ennis by telling about Jack's ideas to settle down with an other guy - if the relationship between father and son was really that bad - which I believe - the son would have never told the old about his ideas.... It's clear from the story that Jack and his father didn't get along. But I doubt that the author would be so devious as to have Jack's father recall how Jack used to talk about bringing up Ennis and then, in front of his wife, fabricate a tale about Jack talking about divorcing Lureen and bringing up a ranch neighbor.
Even before Ennis heard this from Jack's father, we already had hints that Jack was seeing another man ("the sparks flying up with their truths and lies"), that Jack had already been thinking of leaving Ennis ("I wish I knew out to quit you"), that Jack was resigned ("let be, let be") that his relationship with Ennis would never be what he wanted.
It was spring 1983 when Jack said, "I wish I knew how to quit you." That same spring day Jack made his annual weeklong visit to see the old man. Jack "used a come home every year, even after he was married and down in Texas, and help his daddy on the ranch for a week, fix the gates and mow and all.” It was during that visit - within a week after Jack said "I wish I knew how to quit you" - that Jack told his parents he was going to divorce Lureen and move back with a ranch neighbor of his from Texas to help run the ranch.
The old man resented that Jack came only once a year. He really needed Jack full time. He wanted him to live there full time and would not have objected to Jack bringing some other man to live there to help run the ranch.
The old man spoke angrily. “I can’t get no help out here. Jack used a say, ‘Ennis del Mar,’ he used a say, ‘I’m goin a bring him up here one a these days and we’ll lick this damn ranch into shape.’ He had some half-baked idea the two a you was goin a move up here, build a log cabin, and help me run this ranch and bring it up. Then this spring he’s got another one’s goin a come up here with him and build a place and help run the ranch, some ranch neighbor a his from down in Texas. He’s goin a split up with his wife and come back here. So he says. But like most a Jack’s ideas it never come to pass.”
The old man resented that Jack never followed through on his ideas to improve and help run the ranch.
He resented that Jack had left the Lightning Flat ranch and moved to Texas.
"He thought he was too goddamn special to be buried in the family plot.”
His mother Jack told everything about his active sex life as well his relationship with Ennis I suppose. While mothers tend to figure these things out, I believe the prevailing policy between Jack and his parents was Don't ask, Don't tell. As for the shirts hidden in Jack's closet, "stiff with long suspension from a nail", I really doubt that Jack's mother knew anything about them, for if she had found them, she would surely have washed and ironed them and hung them neatly on wire hangers beside the "two pairs of jeans crease-ironed and folded neatly over wire hangers." And had Jack really told everything to his mother, then why did the shirts remain hidden?
Another point about the shirts. These are a token of Jack's first summer with Ennis. They signify how much Jack loved Ennis from the beginning. But I don't think they signify his undying love for Ennis. Jack did not trot them out every time he made one of his annual weeklong visit his folks. By the time Jack moved to Childress, he had more or less forgotten about the shirts. Otherwise, he would have taken them to his home in Childress.
To put her hand on his shoulder is probably the strongest scene of the whole movie - her gesture means something like "forget the old bastard's words - it is only provocation". To show Ennis the way up to Jack' s room should reassure him that Jack really loved him till his last days.The old man spoke angrily. “I can’t get no help out here."
The old man merely resented that Jack never followed through on any of his ideas to move back home to improve and help run the ranch. The old man would not have objected to Jack moving back with another man (Ennis or anyone else) to build a cabin and help run the ranch.
His "Jack, I swear..." goes maybe like that ........I swear, I will always protect you ........., I will always love you................ if I were there you would not have died (you would be still alive) . I miss you so much ................. one day I will bring your ashes to BBM, etc.“Jack, I swear—” he said, though Jack had never asked him to swear anything and was himself not the swearing kind.
Ennis isn't swearing to do anything. He's merely overcome with emotion and at a loss for words (note the hypen).
I doubt that the author would be so devious as to make the reader invent promises for Ennis to keep.