Lots of interesting ideas here. I do believe, though, that Jack was almost resigned when he was rejected by Ennis after the Divorce. He went to Mexico for spite - a kind of ending and new beginning. The conflist (the film and ss are full of confict) is that Jack can't just let go - can't just release him. He does as a pragmatic gesture, but his heart is consumed with this man. After he scold Ennis, the last time they see each other, Jack is venting this conflict and frustration but look at how he reacts as soon as Ennis reacts. He can't stand to see Ennis in pain ... hurt, even at the expense of his own feelings. I think Jack would have gone on with the status quo because he was so consumed with Ennis.
The associated point to all this is that Jack "tried" to disclose to Ennis what he was doing. Ennis talked of putting the blocks on some girl in Riverton. Jack's version is that he is doing the neighbor's ranch foreman's wife or something - when he's actually doing the ranch foreman. I thought this was very telling - Jack wouldn't be able to stand how Ennis would react, but although somehwat resigned, wasn't going to give up even the faintest hint of a shot with Ennis. All yuo have to do is think about how Jack looks at Ennis in his flashback of the 1st time on Brokeback when Ennis hugs him from behind "satisfying some shared and sexless hunger" and Ennis rides away. And ,,, the way Ennis' life ends up, alone, beaten down, consumed with only a memory of what could have been ...