In A Class By Itself by Sandra Brown was published in 1984.
Sandra Brown - In A Class By Itself book description:
Dani Quinn knew Logan Webster would be at her high school reunion. Yet she had come in order to prove to herself that she was not afraid to see him again.
Her departure years before from both Logan and the small Texas town where they were sweethearts had been abrupt, painful, and not of her choosing. Worst of all, she'd never had the chance to tell Logan the truth of why she had to leave. Now she would not only have a chance to explain, but to ask him for a favor.
Handsome, charming, and dangerously charismatic, Logan exudes all the power and confidence of a self-made success. He listens as Dani describes her work for a charitable foundation and expresses her hope that he will donate one of his properties for a much-needed summer camp.
Logan agrees, but with one shocking proviso: that Dani fulfill the intimate promise she made to him years ago. It is meant to be a coldhearted business transaction...but this time when Dani is once again compelled to leave without an explanation, nothing can keep Logan from following.