I think he did. He did mature a lot in those years; might sound a bit macabre but Jack's death might have been the incentive needed for a change in his personality, the missing puzzle piece that helped him realize who he is, and accept himself ...
When you think about it, that's a universal theme in literature and drama including movies: a terrible loss leading to some kind of enlightenment. That's why I'm of the opinion that the ending the producers chose moved it from the realm of sad story to tragedy.
Dingdingdingdingdingding... we have a winner.
Great insights, xvbb and Marge.
This view is maybe as old as Job and common in the Greek tragedies. One learns from suffering.
Not sure I have anything to add on Ennis's "move toward self-acceptance," but I might have something to say about his development.
As others pointed out, Ennis told Lureen that he and Jack "herded sheep one summer on Brokeback Mountain."
And he told Mr and Mrs Twist, "We was real good friends."
[OT: In my opinion, that last sentence really says a lot for Ennis. What Ennis needed most in his life was a "real good friend," and I think that was the most important part of his relationship with Jack. Not to deny the sexual element, but the friendship was ultimately more important.]
Anyway, one thing Jack had that Ennis certainly didn't was a way with words. He can tell off LD, he comes up with stuff like "Friend, this is a g*dd*mned b*tch of an unsatisfactory situation," he just talks a lot. And we all remember when Ennis told a little about his childhood, Jack said it was more than he said in two weeks, Ennis admitted it was more than he had said in a year.
So the long (for Ennis) conversation with Lureen and the difficult meeting with Mr and Mrs Twist are huge steps for Ennis, and in both, he shows that he's learned a bit from Jack how to talk to people and how to get what he wants. As some have said, he basically has to come out to Mrs Twist at least (Mr Twist is clueless) when he takes the shirts.
So he didn't just learn to talk from Jack. He also learned that love is of vital importance. Love is worth taking a risk for. Love is, perhaps, worth dying for.
So he gives a damn whether Kurt loves Jr.
And he makes a way to be at the wedding.
He's has learned (somewhat....still is learning) to value love.