I think that cnr1949 was acknowledging that everyone suffers in these marriages (correct me if I'm wrong) and that it is not just a matter of gay men taking advantage of unsuspecting women but that they're being pressured (even today) to marry in this way. And as tpe and loreen have pointed out, there are so many things that went into Ennis' decision to marry Alma and to stay with her. I agree that he was probably trying desperately to achieve a state of normalcy, not just for appearances but for himself. In the beginning, I think he really thought that he could turn his back on that magical summer, leave it behind somehow and make a life with Alma. But even before Jack returned, it was clear that Ennis was unable to do this, and once they were reunited any hope for normalcy with Alma was dashed. It was undoubtedly easier for both of them, for a time, to stay in an unhappy marriage rather than upset the status quo. There was, after all, no good solution for Ennis, as he believed so strongly that they could never be together, and there were children to be considered. For Alma, she probably held on for a long time to the hope that as upsetting as what she had seen was to her, it wouldn't impact her marriage overall and was something they/she could overcome. I liked the description in the SS of how their marriage came to an end:
"A slow corrosion worked between Ennis and Alma, no real trouble, just widening water.....Her resentment opened out a little every year: the embrace she had glimpsed, Ennis' fishing trips once or twice a year and never a vacation with her and the girls....put her in a long, slow dive..."
You can almost feel her weariness as she finally realizes that this is as good as her life with Ennis will ever get and it just isn't enough. There were good intentions on both sides when the marriage started, which makes it that much sadder that it all ended so bitterly.
I can't say that it's a scene I disliked because it was so well acted by both of them, but I have to admit that the courthouse scene for their divorce struck me hard, as you could see the pain that both of them were going through.
Amazing film, amazing layers.