The Ethical Slut: A Guide to Infinite Sexual Possibilities

Don't be fooled by the title or sub-title. While this book does focus on polyamory, open relationships and more it mostly works on the bases of having a a healthy relationship with communication, honesty, sex, and working out underlining problems like outside influence that could be breaking down your relationship's or your own happiness. This isn't trying to force you into an open relationship lifestyle but if you have an unmovable idea of what relationships or people should be don't read this book.
This book is written with a good sense of humor and doesn't read like a psych textbook or thesis paper.