Desert Of The Heart by Jane Rule

Set in the late 1950s, this is the story of Evelyn Hall, an English Professor, who goes to Reno to obtain a divorce and put an end to her disastrous 16-year marriage. While staying at a boarding house to establish her six-week residency requirement she meets Ann Childs, a casino worker and fifteen years her junior. Physically, they are remarkably alike and eventually have an affair and begin the struggle to figure out just how a relationship between two women can last.

Desert of the Heart examines the conflict between convention and freedom and the ways in which the characters try to resolve the conflict