Somebody has an affair. Betrayal of one's wife or husband is a very bad thing. But it's not the only bad thing about the affair, not necessarily the worst thing. Think of the utter self-falsification which characterizes the betrayer finally. But he didn't start off sunk in self-falsification.
Affairs advance a step at a time, proceeding incrementally.
With each step the situation becomes more complex and more ridden with deceit. At this point someone has cloaked himself in falsehood for so long that he becomes the very cloak he's wearing. Now he's a walking lie. And he no longer knows who he is. Then one day a shaft of light, a ray of truth penetrates the falsity like a laser.