Hello all---
This question has haunted me many times over and I am still struggling with it, but I offer a few comments.
In the beginning of the film there is some beautiful photography of the landscape, and there is a quick scene of three telephone polls. The arrangement of the polls with the cross beams, to me, at least, is evocative of the crucifixion scene of Jesus atop Calvary. I know, I may be stretching this, but in light of the murder of Matthew Shepherd in Wyoming, I wonder if this is a prefigurement to the violent death that one of the characters will meet, namely Jack. I can't take the credit for the connection to the crucifixion. A friend of mine made it prior to my seeing of the film. I used to be a priest so for me, it was a stark and obvious symbol.
Someone also mentioned that possibly Lureen's gross father arranged for the death of Jack by some thugs in order to save the family from the embarrassment of a gay spouse. That certainly is a possibility. However, in the short story by Annie Proulx, there is mention that the father-in-law died and Lureen inherited the business. This was prior to their final meeting in 1983. Maybe that might shed some light on the mystery.
There was also the scene in Mexico where we see Jack spending some time with hustlers. Recall that Ennis gets rather upset when he hears that Jack had been there and warns him that all the things there could get him killed. This might be another prefigurement to the way that Jack died, which was violently as the scene in the movie depicts.
As many of you have said, I suppose it doesn't matter in the end. Jack was gone and Ennis was faced with a terrible void for the love of his life was gone. And that final scene where Jack is alone in that trailer away from any contact with others, is, for me, truly tragic. But there is a beauty to it all. When Ennis says, "I swear," there is an attestation of deep love, and something that he will cherish to his grave.
Liam56