I'm guessing that Jack wasn't seeing the end of the job as the end of their relationship. Ennis was viewing all of this with much more finality. Jack may already have been hoping that Ennis would go off with him and give up on the Alma idea. He probably hoped that Ennis would hop into his truck outside Aguirre's trailer and they would figure things out from there. I do understand why the cheerfulness would be annoying to Ennis. But, this is perfect Jack behavior. He's always trying to cheer Ennis up or provide comfort when Ennis is feeling low/ crying, etc.
Well, I don't mean to be endlessly argumentative (OK, so I AM endlessly argumentative ...), but I can't let Jack off the hook quite that easily. (Sorry, Amanda! Our first point of disagreement!
) Yes, Jack is usually sensitive and nurturing, but this is one instance, I think, where he could have done better. Ennis gave any number of signals that he was really upset: argued that the snow wasn't a threat, complained about the lost wages, kicked the little stream (and the stream, as discussed in an earlier post, may represent their relationship), picked up a log and then tossed it aside in a frustrated way and then, the most obvious one, went off by himself and sat sulking, rather than help with the chores as he normally would.
In response, Jack DOES try to cheer Ennis up, but in such an upbeat, casual way that it would probably just make Ennis feel worse. As far as Ennis can tell, Jack neither understands nor shares his despair. Suppose instead Jack had approached Ennis the way he did after the bear encounter, with a gentle, "Ennis, what's wrong?" Ennis would have hemmed and hawed but maybe eventually given some indication, and Jack would have talked him out of marrying Alma, and they'd go to the Twist ranch and set up a little cow-and-calf operation ...
OK, maybe not. But who knows, it might have changed things.
The excuse people give for Jack, that he probably just assumes they'll see each other again, seems a bit weak. He knows Ennis is planning to marry Alma, and neither has suggested otherwise. If he hopes for some different outcome, his usual approach would be to come right out and say something, but in this case he doesn't. He never makes any mention of getting together again in the near future, or even lingering a little longer together in Signal. Putting the best possible spin on it, that Jack figures they'll meet again next year, still isn't quite enough. Even if another summer on Brokeback were a sure thing, it would still be pretty sad to suddenly and unexpectedly have to say goodbye to the man you love and not expect to see him again for a whole year!
Annie Proulx makes it clear in the story that he can't, even then, look Jack in the face. Cannot admit that it is Jack he embraces.
I don't think this applies to Movie Ennis. He seems to have no problem embracing Jack from the front in either TS2 or reunion scene. In fact, he clearly thinks it's great.
Actually, I'll have to say (hardhat firmly in place) that I think this is a slight flaw in the story; I don't recall even Story Ennis giving much indication elsewhere of feeling uncomfortable with that (on the contrary, the implication is that it's ALMA he doesn't want to see from the front).