tpe, I don't think Alma was bitter. She's the winner with the best husband in the movie. She ended up pretty well off... and loved. Try as I might I can't think of one flaw in Monroe. What a great thing he did by taking on those girls. He was a prince among cheaters, liars and brutes.
And, speaking of folks running kids off, it looks like Alma Jr still lived at home at 19. The child support had ended for her... Monroe didn't boot her out. He could have. He probably gave her a job at the store. The day Alma married Monroe was a lucky day for all of them.
OT: For me, she was definitely bitter. The way she reacted during the thanksgiving scene tell us that she had suffered much and continued to suffer much through all those years of lies, betrayal, and distrust.
Being a winner in the divorce case and being remarried to Monroe does not mean that she was happy -- the same way that there are many people who get pretty much what they want and remain unhappy. Alma did not stay married to Ennis for so long (with the knowledge that she knew) for nothing -- neither did it leave her unscathed. In many ways, she was the greatest loser in this story, if you count how much she suffered/suffers. And as in most betrayals, the pain does not go away after a divorce or a remarriage.
To go back to the topic, one can say the same thing with Ennis -- the loss of his parents at such an early age left their mark on him -- his tendency to brood, to be alone, to be lonely. Clearly, his older brother and sister could not bridge the emotional breach made by the loss of both parents, since they too were immersed in it. Perhaps it is less about heroism and more about desperation -- the will and idea to survive. They all did the best they could, which wasn't that much, I'm afraid.