What is the theme in Bliss by Katherine Mansfield?

One major theme in the story is that of marriage and adultery, specifically, the way in which a couple views their marriage and gages its success. Bertha believes her marriage to be blissfully happy.... she sees it as a strong, loving, partnership.

Harry's affair shatters the image of the blissful marriage.... his indiscretion in their home cements the impression. One question we cannot help but ask is how Bertha could be so oblivious.