Wow. Good topic, good posts.

I guess I'll jump in as well. What follows are my two cents in the form of my free-floating thought process. Bear with me.

First to the anal sex with Alma. The short story does actually refer to this twice. The first time is around the time of the scene in question in the movie.
".....and he rolled her over, did quickly what she hated."Which also implies this was not the first time he'd done so. I don't think it was meant to be intentionally degrading to Alma. I think for him, it was more instinctive and he would probably be loathe to dwell on the why's or who's of what was motivating him. It was, of course, inconsiderate to her nonetheless. Though I find it interesting to note that the passage preceding this shows that he was attending to her needs before flipping her over. So he wasn't completely unaware of her in this sense (which is kind of Ennis in a nutshell - trying to do what he thinks he should warring with his instincts to do things differently).
And I don't think there's any indication that she isn't happy with him and their life per se at this point in their marriage. She just doesn't want to be alone on a ranch in the middle of nowhere. I remember the smile on her face when she sees his truck pulling onto the property.
The other reference in the SS was just before the divorce, when she says of children:
"I'd have 'em if you'd support 'em."Which was also in the movie, except in the SS this was followed by:
And under that, thought anyway, what you like to do don't make too many babies.I really do think that Ennis's instinct to see Jack again was more regardless of anything in his marriage than because of it. It was in the SS that he told Jack it took him a year to figure out that he got sick after coming down the mountain because
"I shouldn't a let you out a my sights."And then:
"Too late then by a long, long while."So he figured he'd let his chance go by and had to stick to his responsibilities. But was obviously still thinking of Jack during that time. While he probably never would have gone looking for Jack himself (Ennis being Ennis), I think he would have been receptive to seeing him at any point in his marriage, no matter how well or not it was going.
As to what Jack was thinking about Ennis during their four years apart, we know that he went back to Aguirre's in the hope of seeing him there the next summer. After that, we see his somewhat clumsy attempts to figure out where he fit in the world and his eventual marriage to Lureen, who was certainly the pursuer in their relationship. Much like Ennis, I think he figured his chance for them was past and he tried to make a go of it with someone else, in a conventional way, as he was 'supposed' to do. But he couldn't forget Ennis, and at some point made the decision to find him again.
Well, they say you never forget your first love. Maybe this was just a pull that neither one of them could resist. Is the timing of their reunion particularly relevant or was it just a matter of time till they found their way back to each other somehow?
I'll stop my Lashawning there. I hope I was coherent enough and some of my jumbled thoughts made sense.