Anyone know this story and can tell me what it is and who it's by? :

A young couple in love. Partner A, however, has sex outside the relationship. B finds out, and it heartbroken. A explains that sex for him has nothing to do with love. B can't understand this. For her, sex is love. B leaves A, and decides that to be able to be with him again, she has to break this idea of hers. So she begins to try finding sex without love. A accepts this, and decides to wait for her. She writes him letters describing her experiences.