It seems like there are some general things we all want: a fountain of youth, wealth, the secret to being happy, and how to be/stay happy in a relationship. Though some are more attainable than others, we have a tip on the happy couple subject. Data on the topic says that whether you're married or not, the happiest couples all think of their partner as their best friend.
John Helliwell, a University of British Columbia economist and co-author of the UN World Happiness Report, studied thousands of couples using data from two of Britain's largest surveys, and found that whether couples were married or not, the single most important factor in determining a couple's happiness was whether the people involved considered their romantic partner to be their best friend. Bottom line, honeymoon phases end, but thinking of your partner as your closest companion correlates to sustained happiness in relationships.