The honeymoon phase with its "high levels of passionate love" and "intense feelings of attraction and ecstasy, as well as an idealization of one's partner," doesn't last forever.

According to a 2005 study by the University of Pavia in Italy, it lasts about a year.

Once you start living together, you realize that you have different priorities and tolerances — like, for instance, what does or doesn't consitute a mess.

"People have to come to terms with the reality that 'we really are different people,'" says couples therapist Ellyn Bader. "'You are different from who I thought you were or wanted you to be. We have different ideas, different feelings, different interests.'"

It's a stressful — and necessary — evolution.

In multiple studies, couples that actively celebrated good news (rather than actively or passively dismissed it) have had a higher rate of relationship well-being.

For example, say a wife comes home to her husband and shares an accomplishment. As we've reported before, an "active-constuctive" response would be the best:

• An active-constructive response from him would be enthusiastic support: "That's great, honey! I knew you could do it, you've been working so hard."
• A passive-constructive response would be understated support — a warm smile and a simple "That's good news."
• An active-destructive response would be a statement that demeaned the event: "Does this mean you are going to be gone working even longer hours now? Are you sure you can handle it?"
• Finally, a passive-destructive response would virtually ignore the good news: "Oh, really? Well you won't believe what happened to me on the drive home today!"

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 out." For instance, one may be nurturing and the other playful.

A 2014 National Bureau of Economic Research study found that marriage does indeed lead to increased well-being, mainly thanks to friendship.

Controlling for pre-marital happiness, the study concluded that marriage leads to increased well-being — and it does so much more for those who have a close friendship with their spouses. Friendship, the paper found, is a key mechanism that could help explain the causal relationship between marriage and life satisfaction.

A study of 3,000 recently married and recently divorced Americans found that age discrepancies correlate to friction in marriages.

Megan Garber reports:

A one-year discrepancy in a couple's ages, the study found, makes them 3 percent more likely to divorce (when compared to their same-aged counterparts); a 5-year difference, however, makes them 18 percent more likely to split up. And a 10-year difference makes them 39 percent more likely.

Over 60% of Americans say that taking care of chores plays a crucial role in having a successful marriage.

"It's Not You, It's the Dishes" author Paula Szuchman recommends a system where each person specializes in the chores they're best at.

"[I]f you really are better at the dishes than remembering to call the in-laws, then that should be your job," she writes. "It'll take you less time than it'll take him, and it'll take him less time to have a quick chat with mom than it would take you, which means in the end, you've saved quite a bit of collective time."

Northwestern psychologist Eli Finkel has found that marriage in America has gone through through three stages:

• Institutional marriage (from the nation's founding until 1850)
• Companionate marriage (from 1851 to 1965)
• Self-expressive marriage (from 1965 onward)

Before 1850, couples got hitched for the sake of food, shelter, and protection from danger. Then with the Industrial Revolution people had more leisure time, Finkel says, so we started looking for companionship in our partners. The '60s brought a yearning for personal fulfillment through relationships, which we continue to strive for today.

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