The Deceivers — John D. MacDonald

Her name was Cindy, and she was his neighbour's wife - the woman next door in the kind of suburbia that didn't make headlines. These were real people, nice people like Cindy and Carl who fought with the desperation of the damned to keep from wanting each other.

Suddenly, though, it was the right time, right place. And there was no room left for pretence. In that moment all innocence drained out of their lives. Two real people, two nice people, became creatures of passion - and guilt.