The Ethical Slut by Janet Hardy and Dossie Easton

The classic guide to love, sex, and intimacy beyond the limits of conventional monogamy has been fully updated to reflect today's modern attitudes and the latest information on nontraditional relationships. 
For 20 years The Ethical Slut has dispelled myths and showed curious readers how to maintain a successful polyamorous lifestyle through open communication, emotional honesty, and safer sex practices. The third edition of this timeless guide to communication and sex has been revised to include interviews with poly millennials (young people who have grown up without the prejudices their elders encountered regarding gender, orientation, sexuality, and relationships), tributes to poly pioneers, and new sidebars on topics such as asexuality, sex workers, and ways polys can connect and thrive. The authors also include new content addressing nontraditional relationships beyond the polyamorous paradigm of "more than two": couples who don't live together, couples who don't have sex with each other, nonparallel arrangements, couples with widely divergent sex styles, power disparities, and cross-orientation relationships, while utilizing nonbinary gender language and new terms that have come into common usage since the last edition.