A 2014 University of North Carolina at Greensboro study found that American women who cohabitate or get married at age 18 have a 60% divorce rate, but women who wait until 23 to make either of those commitments have a divorce rate around 30%.
"The longer couples waited to make that first serious commitment [cohabitation or marriage], the better their chances for marital success," The Atlantic reported.
The 'in love' phase lasts about a year.
The honeymoon phase doesn't go on forever.
According to a 2005 study by the University of Pavia in Italy, it lasts about a year. After that, levels of a chemical called "nerve growth factor," which is associated with intense romantic feelings, start to fall.
Helen Fisher, a psychologist and relationship expert, told Business Insider that it's unclear when exactly the "in love" feeling starts to fade, but it does so "for good evolutionary reasons," she said, because "it's very metabolically expensive to spend an awful lot of time just focusing on just one person in that high-anxiety state."
Back in the 1950s and '60s, Canadian psychologist Eric Berne introduced a three-tiered model for understanding a person's identity. He found that each of us have three "ego states" operating at once:
• The parent: What you've been taught
• The child: What you have felt
• The adult: What you have learned
When you're in a relationship, you relate on each of those levels:
• The parent: Do you have similar values and beliefs about the world?
• The child: Do you have fun together? Can you be spontaneous? Do you think your partner's hot? Do you like to travel together?
• The adult: Does each person think the other is bright? Are you good at solving problems together?
While having symmetry across all three is ideal, people often get together to "balance each other." For instance, one may be nurturing and the other playful.