A relatively pessimistic POV, but certainly has more than a bit of truth.
I personally tend to think that people simply become more comfortable with each other as time goes on (or not), and this replaces passionate/romantic love.
Sure. I don't think that one excludes the other. Love changes shape, but it can not develop and endure if the image that we created shows up to be completely wrong one. We have to have at least a part of the man/woman we dreamt about.
The image Alma created about Ennis was not wrong, but Ennis was not right. He also didn't know at the beginning that their relationship would go terribly wrong. I believe that if he knew it, he would've never marry Alma.
And here I agree with LNJ:
I agree, it is unpleasant but she had every reason to devalue him - actually she didn't need to do that - he did that on his own when he broke his vows. And again, I don't think he ever intentionally hurt her, although by not considering the impact of his actions on her he was, in effect, devaluing her long before she began to lose faith in him. There are a lot of dynamics in place there, resulting in Alma feeling the way she did.
Her love for Monroe..

... I just can see love there. She came bitter, disappointed, from the marriage she wasn' t respected at in full. Monroe was always so understanding to her, so nice to her and kids... The circumstances show me that her marriage with Monroe is not the result of love. And Monroe was ( I believe deliberately) shown not as the most attractive man on the Earth.That's also a clue. I can't see no real love, real feelings form Alma there. Real home, real money, house, peace, security... but love in it's magic, IMO no!
Scene on Thanksgiving day at the table was extremely unpleasant cos Alma was striking and rolling with her eyes, and I just can't understand why did she ever invite Ennis for dinner? It was obvious that Ennis is very uncomfortable too. Finally the kitchen scene was the culmination of displeasure and we know the rest. Ennis ends up beaten.
Why do you think they invited him for a dinner? Because of the girls or they just felt sorry for him?