I would like to recommend www.StrongFamilies.com (which has wonderful resources for improving relationships).
In particular, the books:
The Two Sides of Love by Dr. John Trent & Gary Smalley
The Blessing by Dr. John Trent, Gary Smalley, & Kari Trent Stageberg
Dr. Trent’s children’s books are also wonderful.
When you get to the website, click on “The Store” for resources.