Facing Love Addiction: Giving Yourself the Power to Change the Way You Love by Pia Mellody
First published over 15 years ago, this book is still the go-to resource for understanding love addiction and love avoidance. Pia Mellody masterfully lays out a clear understanding of how the attachment patterns of love addiction and avoidance manifest in relationships, helping the reader identify each step in these two relational cycles. I often encourage clients to read this book with two different highlighters in hand. Use one color to highlight those things that seem true about you. Use another color to highlight those things that seem true about your partner(s). This will help you to get a clear picture of how these two attachment styles interact with one another in a relationship.
Healing the Shame that Binds You by John Bradshaw 
This is another classic published many years ago by a leader in the field of addiction recovery. Anyone with a history of either addiction or trauma can benefit from this book as Bradshaw takes on the uncomfortable topic of shame: often the root of addiction and the core of trauma. Bradshaw differentiates toxic shame from healthy shame (what we often today refer to as guilt). He helps the reader to understand the way that toxic shame impacts their relationship with both themselves and others. He then points the way to a different way of being that is free of toxic shame and its damaging effects.