Hi All...
Well, the "Jack I swear, I should've never let you out of my sight." said in the motel room is enlightening, but in the book when Ennis says "Jack, I swear.." at the end, Annie also adds word to the effect (not a quote) "....though he never was one to swear, nor did he ever ask Jack to swear anything." and that further adds to the "openness" of the line "Jack, I swear..."
And of course the book does go beyond the line and on to his dreaming about Jack and the revealing line, "There was some open space between that he believed and what happened, but nothing could be done about that." And the last line of the book, is that "realist" statement of Ennis's "And if you can't fix it, you gotta stand it." It's interesting that the movie didn't go on to Ennis dreaming etc, but uses the "Jack, I swear..." as the end. It does really leave the ending open and more mysterious. Anyway, I'm enjoying what others are saying here. Thanks!
Rayn