Well, get back from that meeting and elaborate, Jeff! I am so pleasantly amazed that you are agreeing with me I want to draw out the moment.
Actually, there really isn't anything more for me to say than what I've already said
ad infinitum (or is it
ad nauseam?). The implied threat in Jack's "wish I knew how to quit you" line may trigger Ennis's collapse, but Ennis's response is out of proportion to Jack's comment in and of itself and is accounted for by the release of everything he's been suppressing and denying for twenty years, including but not limited to his love for Jack, as a result of his internalized homophobia. To attribute his collapse
solely to his fear of losing Jack, which certainly is one factor, or to
any one cause or reason, or even to try to assign one most important cause or reason, does a disservice to the film, to the writing, and to Ennis.
Paradoxically, fear of losing Jack may play a larger role in the collapse of Ennis in the story, who is not as complex or as repressed a character as Ennis in the movie (he's perfectly conscious that Jack is the love of his life, and has been conscious of it since about 1964, but he just won't act on it), but I don't think it's the single cause of the collapse in the story either.