This maybe a little over my head, I have to admit I've been a "subject", to a lot of verbage, "Are you getting up?" "Are you going to work?" "Are you going to clean the kitchen?" "Yes, I am lazy.", lol
Seriously, I read these posts, I'm not that organized in writing my thoughts, but they sure as heck got me thinking, but here it goes, any way. Jack never made Ennis swear to anything. He wanted him, in my view anyway, to commit to something, but by his own will. Jack let him off the hook after that first summer, he let him off the hook at the reunion, he let him off the hook at the final meeting. No commitment, no swearing to anything. We see what the lack of that commitment could do to a relationship. Jacks cruising in Mexico, and Ennis living an unfulfilled, unhappy "hetero life", brought on by fear, and fuel by hook ups once a year. That one sentence: "Jack, I swear--" he said, thought Jack had never asked Ennis to swear anything was himself not the swearing kind. To me this was the whole answer to what tore at them. Did Jack know that Ennis was not the swearing kind? He did. Jack never asked him to swear to anything, it had to be a total independent action, I swear to you my life, I swear to you my love, Ennis never did any of those things, at the time it wasn't in him. Its kind of nice to think without declaring it, it was ok, but to Jack it wasn't, he wanted more, always did, but wanted Ennis to want it to of his own free will. Like the men that they are.
The irony is, "Jack, I swear", love between men is fragile at best, and can be devastating to us if it goes wrong. We have our "male pride", our "independence", the things we love about ourselves and in each other, fear of showing anything less to some of us is worse than death, in turn not letting our guard down, letting go of the fear of rejection, or the fear that we have love for another man, we sometime loose what we wanted most.
Ennis not a swearing man, sworn himself to Jack, and Jack comes back to him in his dreams.
MHO