MisRed, this is one of the most tearjerking but utterly beautiful posts i have read. It hadn't really occurred to me in that way before, i'm usually in a mess by then, but the way you have put it makes total sense. Thank you for a truly gorgeous post. 
thanks, aimi15!

But it's because of eveyone else here at ej that these things come to mind ...
Reading what everyone else writes here gives me new perspectives and insights, makes it seem like I'm watching BBM with fresh eyes each time ... something you couldn't nornally say about something you've seen 27 times!

And to me the shirts prove that Jack would've still saw Ennis, even if he tried to have a life with someone else. The shirts to me is like an unconditional love Jack had for Ennis and no one could change that. In the scene, after the flashback and the look on Jack's face, to me Jack is thinking that his dream with Ennis is dead. So he can try to find someone to share his sweet life. But the shirts prove Jack would've still saw Ennis even after trying to have a life with someone else. That is why I believe the November trip would've been the big ultimatum-the decision that would change the course of their entire relationship. If Ennis knew Jack was having a life w/ someone else, he would've been on fire. However, what Ennis would've done is totally left in the air. He probably would've killed Randall in his sleep. And have that life with Jack.
Interesting point, browneyes, about Ennis being "on fire", and an apt choice of words, I think.

For all that he's often spoken of as being the quiet one, his intensity does burn through, particularly in anything to do with his relationship with our Jack.
Just the way that he switches the shirts around so that his own is now covering Jack's, speaks to the protective instincts he has always had inside, trying to keep Jack safe. Ultimately he had been unable to shield Jack from being hurt by the world - and indeed Ennis had a hand in the hurting, mortal blows aside. Sometimes I see this reversal of the shirts as being an apology to Jack for that hurt he suffered due to Ennis's fears, as well as a promise that Ennis's love would have been there for him always, regardless of those last words spoken.
Don't know that I think Ennis would go as far as to kill Randall in his sleep, though ... Now, in a bar fight maybe ...
Like you, many of us want to believe that Ennis would one day have decided to have that sweet life with Jack ... and we can speculate on what might have one day made him change is mind .... left up in the air, as you say, because of Jack's life being cut short.