Wow what an insightful post, Clarissa and everyone. My feeling is that Ennis blows up like that not because of jealousy or homophobia but fear of losing control and being found out. He wants to keep Jack on a short leash that doesn't reach to Mexico. Also he is starting to panic because he sees Jack weighing over things in his mind, and it dawns on him that Jack might make a move to change things. Ennis can't stand the thought of anything changing, especially suddenly. No, he's not fooling and if he can't get control of himself he might hurt Jack. A man who might punch, or even threaten to punch a pregnant lady could do anything. However his threats do not dissuade Jack in the least. He forges on with the best weapons he has, words. "We coulda had a good life...but you didn't want it, Ennis. And now all we have is Brokeback Mountain. F**king all. Everything's built on that."