I have to admit that I have much more empathy for jack than Ennis, he waited not 1, 5, but 20 years, as far as I'm concerned I couldn't have waited so long, even if my love for someone had been great, I would have been devastated but for my own sanity, I would have move on. What I think is tragic, it's the context, the homophobic environment where they both leave and grew up. So for me 20 years it's far too much. Jack was the one who tried to find solutions to their problems, " we should move to another place, an another state, maybe south, maybe Texas" He was willing to do that all the time. But each options of Jack were roughly rejected by Ennis. I can't blame Jack to have search solace in the arms of other men, it was just human. On the other hand, Jack was the talkative one, the extrovert one, he should have been more open to Ennis concerning his love, he hide the shirts, didn't say clearly that he loved Ennis. Sometimes I wonder why he waited 4 years to send this damn post card! 
When you're deeply in love, you mustn't wait so long, it was 4 years of irreparable damage. Ennis was surely in the closet all this years untill he found the shirts, but Jack too in a way in not expressing verbaly his love! shit, I'm going to cry again now 
I am a bit slow replying to this. It got me thinking on a couple separate tracks.
One is the concept of waiting for someone to change. I think it's safe to say, we cannot expect the person we love to change for us. We have to take it or leave it. We can take it as is, and bask in the love of the moment. Or, we can pursue our life according to our expectations. Love cannot abide by other people's expectations. True love does not expect our beloved to change for us. True love is when we willing change ourselves for our beloved, no strings attached, no conditions amended, no expectations in return. Ennis made that mistake in his homophobia (living up to his pop and society's expectations); Jack did the same waiting on Ennis to change. Truth is, they had a good thing going. They could do more, but love is happy with what is, not what might have been. Waiting for 20years? True love waits a life time, and not regret a minute of waiting. Yes, it coulda been a sweet sweet life with the cow and calf operation, but Jack's ideas are often filled with bluebirds singing next to whiskey springs. The beauty of their relationship had always been the practicality of Ennis bringing the dreams of Jack to reality. Jack wanted elk? Ennis shot it. Jack wanted to stay closer to camp? Ennis wouldn't mind switching. Jack getting bored of just sitting around the camp fire? Ennis brought his horses for exploring the wilderness. Jack didn't like the cold in November? Ennis managed to get Don Wroe to lend them his cabin. When Ennis said "no" to Jack's dream, it was not for nothing, but for his deeply rooted fears and societal reality of that time. If Jack cannot accept Ennis the way he was, then what can we say about Jack's love? It's all about him, and Ennis was just along for the ride? I think not. Jack understood Ennis and accepted that. That's the tragedy. Jack kept on dreaming, waiting on Ennis. But his patience ran out, just as Ennis, and social mores (they were coming up on the Stonewall riot and the liberation movement when Jack died) were about to change.
Secondly, I don't think either of them thought about this as love, but more as sex and passion. The conversation in the motel was all about stemming the rose hundred of times when they were apart. Jack said he could hardly stand it, but what did he do to help to stand it? Going off to Mexico. It was never about love, consciously, except for a few moments. Jack was in denial just as much as Ennis was, but he was willing to flaunt society for sex...prostitutes and all. Ennis was more conservative, and never realized what it was, until Cassie said, "Girls don't fall in love for fun." Cowboys have fun, but fall in love for more than fun, too. So why did Jack wait four years before sending his postcard? Recall the scene at the hospital after Bobby was born. He was treated like dirt by Old Man Newsome. His wife did nothing to stand up to her father. He felt alone in a room full of people, with a baby, his own son, looking like the Old Man, so the Old Man says. Both of them found companionship where none was expected up there in the mountain. In their loneliness, they yearn for each other, and held onto each other, for twenty years, and didn't know how to quit, didn't want to quit. It's a wonder Jack waited so long before sending that postcard, but then again, he did go back to Signal looking for Ennis...but that dang Aguierre put him in his place...you boys weren't paid to stem the rose while the dogs babysat the sheep. Jack had his fears, too. So let's not blame it all on Ennis.
