All About Annette by Alan Marshall; Donald E Westlake

Sometimes wild, sometimes willing, always wanton. An incredible triangle and a woman who couldn't stop cheating.

From the back cover teaser: 'The husband. Charles could resist anything except temptation. He loved his wife but couldn't stop cheating. The sister. Claire found fulfillment in the lush jungle of the third sex. but there was only one woman she ever really loved - her brother's wife! The wife. Annette was driven by her husband's unfaithfulness to look for love elsewhere. Her husband was weak, and Claire, who really loved her, was a lesbian. No wonder Annette turned to.'