This is one of the three books I use for couples work and recommend to all of my clients, friends, and family.

In this insightful book, celebrated research psychologist and couples counselor John Gottman plumbs the mysteries of love and shares the results of his famous “Love Lab”: Where does love come from? Why does some love last, and why does some fade? And how can we keep it alive? Based on laboratory findings, this book shows readers how to identify signs, behaviors, and attitudes that indicate a fraying relationship and provides strategies for repairing what may seem lost or broken.
https://www.amazon.com/What-Makes-Love-Last-Betrayal/dp/1451608489