TL;DR
Three Harsh Truths About Love : Love does not mean equal compatibility, love does not solve your relationship problems, love is not always worth sacrificing yourself for.
Review
To be honest if you ask me whats the greatest book on relationship dynamics? I would blindly suggest this to you. Its compilation of case study of 5 peoples who are dealing with some kind of problems in their relationship and we hear their journey about improving them.
There is a lot to take on from this book. It challenges the idea that love alone can sustain a relationship. There are things more important than love in a relationship like values, compatibility, and personal responsibility which are far more important in the long run. Its a practical, no-nonsense take on relationships that pushes you to think beyond just feelings.