Polyamory

There's an interesting fictional treatment of polyamory in "Design for Loving" by Doug Sanford. The story begin with what seems to be a friendship/relationship between a straight college student and a slightly older gay man but soon develops into an interesting polyamorous situation. You can find a review of it on Goodreads at https://www.goodreads.com/book/show/44147006-design-for-loving I enjoyed it.