This is just a place holder for some articles I've found. It is not even scratching the surface of the subject.

Stages of a Romantic Relationship:
How to Assess Your Relationship Stage: 6 Steps - wikiHow
Including marriage:
The 5 Relationship Stages
Love:
See the love page.
When to use the word love in a relationship

Links:
Love-sessions.com
The 5 Love Languages web site (A different 5 - Words of Affirmation, Quality Time, Receiving Gifts, Acts of Service, and Physical Touch.) by marriage counselor Gary Chapman
How Do I Love Thee? Experts Count 8 Ways | LiveScience
  Love Language Quiz
Does the L-Word Belong in Business?
Widower Dating