The four year separation was almost an affirmation at the reunion of what they had in '63 was real, and neither never recovered from it, nor sought to be cured of it. But it also showed just the way it was going to be between them, after all it was Jack who who sought out and bought Ennis to life, but it was Ennis who kept Jack in a reality that at times could tear them apart.
IMO: Separation in their relationship. Sometimes I looked at the separation in the years that followed the reunion, as such a unnecessary self-imposed exile from each other. Not by any outside force, but by their own design.
The remarkable love they showed and had for each other, could be followed the pain they could inflict on each other, and pain they inflicted on themselves as individuals in a week that maybe happened once or twice a year.
Separation could be a two edged sword, it may lead to appreciation, an honesty, but also deep resentment, anger by one who may feel slighted after a while. Jack felt that way, Ennis couldn't understand that because separation in his mind kept him and Jack safe. "We could get together every once in a while", as long as they could hang on. Jack was tire of just hanging on he wanted more than that, but Ennis was going through his own kind of hell. The final confrontation, that moment had to come, it was inevitable.