Intimacy and Solitude
by Stephanie Dowrick is not a book about polyamory, but I'd recommend anyone to read it. Stephanie's premise is that our happiness depends on a healthy balaance of intimacy and solitude (that is, being happy to be intimate with others, being happy to be intimate with ourselves), but that for reasons of fear etc. we often tend to settle for attachment and isolation instead, as poor subtitutes that we believe will keep us safe.
This book has certainley helped me in considering why I want to be in the relationships I want to be in, and why I want to be on my own