It was a friendship that became a secret.
I am not so convinced by that one. Initially I would agree,but Jack knew the 1st year after BBM that they had been observed.At the reunion Ennis and Jack are observed by Alma.Also although not in the film but in the S.S ,Jack tells Ennis he thinks they may have been observed on BBM.
Ennis thinks people look at him funny and guess, not about him and Jack but certainly regarding his sexuality.
I am sure that Lureen has guessed and also OMT and Mrs.T infer that they knew, at that fateful meeting.
So I agree that initially as far as Jack and Ennis were concerned it waS a secret,but little by little as the film unfolds,it becomes apparant that more and more characters are aware of "the secret"
I often feel, considering OMT knew, how much easier to set up together it could have been,than Ennis was thinking.They would have been right out in the middle of nowhere,licking the ranch into shape.With OMT there ,I doubt they wiuld have suffered the fate of Earl and Rich.
Every time I watch that scene,where it becomes apparant that both the Twists knew,I wonder what goes through Ennis's mind.He now is aware that Jack was serious enough to talk to OMT about it,although I suspect not in full detail. Ennis then discovers the shirts,does he think,maybe Jack was right,we could have done it, way out here in the middle of nowhere, and these two shirts would have people in them still.
It is interesting that OMT never says ,over my dead body or something like,he just says "like most of Jacks ideas it never come to pass." You would think if he was such a homophobe and so against it,he would just have told Jack in very plain terms what he could do with that idea.