What keeps the man and woman together?

The man and the woman in Katherine Anne Porter's short story "Rope" are going through a stressful point in their relationship. It seems that they have only recently moved to the country, and the woman in particular is finding country life trying. She is irritated with her husband for returning from the store without one of the small pleasures she had been looking forward to, namely, coffee. However, there are flickers of a better relationship between the two of them under different circumstances. The man rubs his wife's shoulder, remembering that "when they were playful," she would "arch and purr" in response to such treatment. This is not how she is behaving now, but the husband knows that this is not always her way.
As the argument continues, it becomes clear that the two have communication difficulties. The woman once told her husband that her happiest period in two years had been two weeks spent away from him; she clarifies that she meant she "was happy getting the devilish house nice and ready for him," not because they were apart. The husband tries to remind his wife of the "fun" they once had, which the wife now seems unable to think about.
At the end of the story, we see the calm after the storm. In the end, the woman, who was once so upset about the rope, tells her husband she doesn't want him to exchange it "if it [is] something he really want[s]." Now, her mood has changed: she has her coffee, and she thinks it "fine to be here." Her husband is "a love" in her eyes, and the man thinks that she had been upset earlier simply because she hadn't had her coffee. He observes that "he knew how she was." The implication is that the woman's moods are extremely fickle, but this is simply part of her personality.
Without more context, it is difficult to know whether this argument represents an ongoing pattern in the relationship, with the man staying with the woman out of a hope for warmth between her periods of irritability, or whether she is simply behaving like this at the moment because of their stressful situation. Certainly, the husband seems to stay with his wife because he does not really believe she means the things she says to him, and he looks forward to the times when she behaves fondly toward him. For her part, the wife will have different reasons to stay with her husband. For a woman to leave her husband would have been a difficult prospect to begin with: moreover, while she is angry with him in this story, she ultimately seems to feel that he is "a love" and knows that he will do what she needs and wants in the end, even if he is forgetful and selfish at times.