Tell you what, reading the first part of the post, I was reminded of a comment Annie Proulx made about both Alma and Lureen learning some hard lessons about life. Maybe Ennis was initially Alma's dream man; I'm not sure we can know that, even though she married him. Yet from her perspective he turned out to be a dud. Settling is a sad word, however accurate it might be. As a divorced mother of two with no education and no prospects in the Wyoming of the 1970s, she could have done a lot worse than a sweet guy who loves her and can provide some financial security for her and her kids, not to mention a much better home than that cruddy apartment--even if it is a bit fusty and old-fashioned.
I'll let someone else address the concept of stability, although I wonder whether security might be a better word here.
Good point, Jeff. A even happier spin on it might be that Alma is established early on as someone who places importance on financial security and the comfortable life it buys. She cajoles Ennis for an apartment in town, takes a job (the story's "saw she'd always have to work to keep ahead of the bills on what Ennis made" suggests a certain bitterness), warns Ennis against upsetting the foreman, says she'd have kids if he'd support 'em, promptly marries Monroe after their divorce. It's possible that Monroe provides her the very life she always dreamed of.
I'm not doubting that she loves Ennis. But how much evidence do we have, really, that in her eyes he was ever such a superior catch to Monroe? The only thing I can think of is to show her less than happy with her later lot in life is her sour mood at Thanksgiving, but there are other explanations for that. Beyond that, we might be projecting our own preference for Ennis onto her.
After all, she married Ennis without knowing him very well ("more than I've spoke in a year"). Even early on, at the wedding, sliding, when the girls are sick, even in bed that night, there's no really strong evidence that Ennis is the absolute love of Alma's life. She doesn't seem particularly happy or passionate. For all we know, she may have gone -- given her era, probably DID go -- into marriage imagining that their life together would be a comfortable, middle-class, white-picket-fence existence, that is, featuring the comforts that life with Monroe eventually has.
It's true that we don't know a lot about what Alma's personal dreams (I mean her vision of her personal "sweet life" or "cow and calf operation") might be. Maybe they never extended beyond a simple life in Riverton as a wife and mother.
I would guess that's true. She's not well educated or sophisticated, it's the early '60s, and she lives in a small town, all suggesting that a simple life in Riverton as a wife and mother was probably exactly her vision of the sweet life.