There are many books and resources with information on building and maintaining healthy relationships, such as:

A Couple's Guide to Communication by John Gottman

Extraordinary Relationships: A New Way of Thinking About Human Interactions by Roberta Gilbert

Relationship Rescue: A Seven-Step Strategy for Reconnecting with Your Partner by Phillip C. McGraw

The Relationship Cure: A Five-Step Guide for Building Better Connections with Family, Friends, and Lovers by John M. Gottman and Joan Declaire.