While it is clear, and unavoidable, that the majority of fan fiction readers take the route of a "happily ever after Jack and Ennis", the commitment to an orthodoxy model means that this majority dictate what constitutes an "acceptable plot." One of the concepts is the concept of the "One true pairing" which means that the only pairing that is acceptable to be depicted, and the only one that makes the story "a real BBM fanfic" is a Jack and Ennis pairing.
But since Jack dies in the source story, the possibilities for writing in this pairing are limited to the period in which they were alive (infrequent meetings), or after Jack dies, which convicts Ennis to a life of lonely mourning. Not exactly a wide field for exploration of same sex relationships if one follows this model.
The germ of the notion of the "one true pairing" is that once one has had a relationship with a soul mate, there can be no one else. Or, in Ennis' case, anyone else would be basically 'Jack Lite.'
But that isn't how human psychology works. Sometimes people do swear off relationships after a soul mate dies, especially if they're quite up in years although that isn't universal by any means. And generally, if a person Ennis' age (39 or 40 when the original story ends) foregoes other relationships they're either going to find some new center of their life: family, creative work, career, etc. or they're at risk for a downward spiral of depression and possible suicide. And a new relationship isn't necessarily a "replacement" for the soul mate, as if any human being can be replaced anyway. Marriages and other long-term commitments start up for all kinds of reasons and a huge amount of acreage of middle ground exists between a
grand passion and decades of depression, isolation, sackcloth, ashes and alcohol. A second pairing can certainly include love and sincere commitment, and sometimes with the participants having learned and matured via the earlier relationships.
That whole question was brought up in the 'would Ennis commit suicide' thread, and it's certainly a high risk, how high possibly depending on his ongoing relationship with his daughters and possibly grandchildren if he never did meet anyone else. But it's by no means a done deal that Ennis would become a gay male Wyoming version of Queen Victoria wearing mourning for four decades.
The fan fiction philosophy here is that if it is based upon or uses characters from BBM - then by all means write it and post it. My limitation in writing fan fiction stories is that I can't find it in me to rewrite Annie's ending of the story, and so therefore, Jack dies. Even though I have deeply enjoyed writing Jack flashbacks, and Jack-as-a-ghost in my first story "A Warm Wind Blows", somehow, the idea of resurrecting Jack or diverting the end of the story... eludes me to date.
There are quite a few AU stories I've liked so far, including
Somebody New and Madlori's "Farmingdale" series; i.e.,
Human Interest followed by
Two Crows Joy. Generally I do like the ones that keep the characters' background, though; can't quite get into the idea of Ennis and Jack on the Titanic, in 1930s Berlin, in Paris, etc. At present, I'm trying to read HI simultaneously with your Laramie saga, which means a lot of reading!
What I do object to, and find destructively dogmatic and limiting, is the notion that Ennis in an alternate universe union with Jack or Ennis as a depressed alcoholic are the only "acceptable" alternatives. Insistence on the latter in particular sometimes has a distinctly vindictive cast to it.