Every Successful Relationship Is Successful for the Same Exact Reasons
Relationships exist as waves - we need to learn how to ride them. Some waves last for hours, some for months or even years. The key to success is to understand that few of those waves have anything to do with the quality of the relationship.
People lose jobs, family members die, couples relocate. You may go through times where you may not feel "in love" and times where you love your partner more than ever. Your job as a committed partner is to simply ride the waves with the person you love. Because in the end, none of these waves will last.