(for all Ennis knows, the other fella is someone Jack met and fell in love with AFTER seeing Ennis the last time -- at least we have reason to think otherwise),
Jack went up to LF immediately following his last trip with Ennis. In fact he told Ennis at the truck that he was gonna head up to LF for a day or two.
I have always assumed that when Jack's father told Ennis " then this spring he says he's gonna bring another fella up here to whup this ranch into shape, blah blah blah" - well I have always thought that Jack said this
on that self-same visit to LF, the day after leaving Ennis for the last time. Doesn't Ennis also think the same thing, that it was the very next day?
I have seen lots of posts inferring that this or that happened between the time of their last fishing trip and the time he told his parents about bringing up some other guy, but I believe that from what we've been shown/told that both trips were one and the same trip for Jack. In other words he had the long drive up to LF to mull over his life and what to do about it, cried about Ennis I'm sure, and was trying to work himself up to doing something to fix a goddamn bitch of an unsatisfactory situation.
Is there a flaw in this logic, people? Why do so many Brokies think that there was a time lapse between the two events?
Thinking of leaving Ennis, telling his parents about the change of plans, and actually accomplishing the feat of severing ties with his beloved Ennis are entirely different matters, I don't know if Jack would have actually succeeded in leaving his other half, but I think he was thinking on it, that is why he said what he said to his Pa, just like Diane has explained so well.