I have always felt that when Ennis got divorced he was in a way relieved and went off into a secret world in his mind where he could be as available to Jack as he could manage. It meant a lonely existence for him and no guarantees, but that is not answering your questions I know.
Yes, I think in many ways it is about standing it. They had hard lives and the story hinges on this one dynamic, their attraction to one another and how that made their lives harder.
We all walk around with our secrets. Sometimes, they are our only company.