Left Hand of Darkness. Lowell, Jax Peters. The Same Embrace. The Last Resort. The first book in the fantasy trilogy, Chronicles of Tornor, has several gay and lesbian protagonists, both as main characters and in supporting roles.
Main characters are gay men but sexual matters are treated very tactfully.
Fall On Your Knees. A Canadian bestseller published in 1997 includes a main character who has a lesbian relationship portrayed in a loving, positive way, though it is not a major theme of the novel. It's a wonderful book. Cherry Aimless Series. The Good For Nothing Girl Friend.