Alma was the one person in the film I felt was least honest about her feelings to anyone, including herself. Even Ennis, who had immeasureble trouble being outward about his feelings, was able to find a work-around to attend to his separate life.
One one level, Alma must have felt Ennis was her whole life; her man, her world. the scene in the grocery when Ennis brings in the two kids tends to underscore this. On the other hand, she never ever did a single thing (other than divorce that I bet Ennis had no clue why) to try to win Ennis' attention back.
Alma, even 16 years after she witnessed Ennis and jack together in the stairwell and years of fishing trips, said "the girls and i think you should get married". And after she made a somewhat elaborate "gotcha" claim about the fishing tackle box and never coming home with fish, she failed to state affirmatively that she SAW the men together. Ennis never knows what Alma knows.
I think Alma's feelings for Ennis center on what she had hoped he'd be and what she dreamed she'd have. In the end, she allowed her anger and sense of rejection to build to a level of detest for both Ennis and Jack.