Hi, everyone. I've enjoyed reading the discussions here, and I'm looking forward to more!
What we know for sure about Ennis is his investment in "the way things are supposed to be." His struggle is reconciling his reality with his "supposed to's.: He's supposed to get married, supposed to have kids, supposed to have a family, supposed to support them, supposed to be there when the calves are born, and supposed to not love another man. He doesn't have a clear picture of how he's supposed to do all that (since his parents died and he was raised, then more or less abandoned, by siblings) and he's keenly aware of how he's failed in all of the "supposed to's."
I saw the grocery store scene and the extra shift scene in that light. In both, he's being slapped in the face by his own failure to meet that standard. If he was making enough money, his wife wouldn't have to go to work. If he had succeeded in doing what he was supposed to do, she'd have been at home taking care of the kids. It's not about whose job is more important, it's about his realization of his own inability to be a good man (according to the unrealistic standard that he perceives to have been set). His real anger is toward himself, and because that's too uncomfortable for him to acknowledge, it is expressed at Alma, the evidence of all his failings.
I hope that doesn't sound too psychoanalytical. That's just kind of how I see the character.
Marty