Love relationships and the people in them go through stages. A couple may progress through the stages together or one person may be in a different stage from the other.
Symbiosis—spend time together noticing all the things you have in common, loving everything about the other person.
Differentiation—noticing differences and becoming annoyed with some of them. Arguing about issues. Growing awareness that you are unique individuals in a relationship together. In this stage you need to find ways to deal with differences and conflict.
Practicing—spend time focusing on oneself: work, activities, friends outside the relationship.
Rapprochement—the couple turns their focus back on each other and enjoys renewed closeness.
*This is a fairly technical book written for therapists. It is a relatively easy read. Bader, E. and Pearson, P.T., 1988. In Quest of the Mythical Mate: A developmental approach to diagnosis and treatment in couples therapy. New York: Brunner/Mazel Inc.
Emilio Escudero has an excellent, useful summary of the stages athttp://emilioescudero.com/files/StagesInTheDevelopmentOfACouple.pdf
The book is available athttp://www.couplesinstitute.com/in-quest-of-the-mythical-mate-textbook/$42 andhttp://www.amazon.com/Quest-Mythical-Mate-Developmental-Diagnosis/dp/1138004596$12-$69.