From “sex recessions” to a dip in the divorce rate, there was no shortage of interesting findings and trends about relationships in the 2010s.

As the decade comes to a close, we look back on 11 of the most interesting things we learned about love and relationships from the world of social science.

1. Women are happier with less attractive men.

Maybe all those CBS shows about schlubby leading men with hot wives were onto something: A 2017 study out of Florida State University found that in successful relationships, the woman is generally more “aesthetically gifted” than her partner ― and that women are happier with less attractive men.

In the survey, a group of 113 newlywed couples were rated on their individual looks. The researchers found that if the male was less attractive than his wife, he was much more likely to compensate with gifts, sexual favors and doing chores around the house. Unsurprisingly, that lead to higher marital satisfaction for the wife.

“The husbands seemed to be basically more committed, more invested in pleasing their wives when they felt that they were getting a pretty good deal,” said the study.

The researchers also found that “less attractive” women were more motivated to diet and be thin if their husbands were good looking.

“The results reveal that having a physically attractive husband may have negative consequences for wives, especially if those wives are not particularly attractive,” lead researcher Tania Reynolds said.

2. If your ex wants to be friends, they might be a psychopath.

The next time your ex asks “can we still be friends?” you might want to be wary. In 2016, researchers from Oakland University in Michigan found that people with the so-called “dark triad” personality traits ― like narcissism and psychopathy ― often keep their exes around for calculating, self-serving purposes.

A desire for continued sexual access, financial help or a need to still exert some control over a former partner were among key reasons for maintaining contact, especially for men, according to the study.

3. Male gay couples stay together longer than heterosexual ones.

With gay marriage comes gay divorce? Social scientists had a whole new demographic to report on as same-sex marriage was legalized across the country as of 2015.

In 2018, a study by The Williams Institute at UCLA examining same-sex and heterosexual couples over 12 years found that gay couples were the least likely to break up. Lesbians were most likely to break up and straight couples were somewhere in the middle: female-female couples (29.3%) were twice as likely as male-male couples (14.5%) to terminate their relationships, compared to 18.6% of male-female couples.

4. We might be in the middle of a millennial “sex recession.”

People in their early 20s were two-and-a-half times as likely to be abstinent than Gen Xers were at that age, the story said, and 15% reported having had no sex since they reached adulthood.

It’s not just millennials whose sex lives have taken a hit: From the late 1990s to 2014, sex for all adults dropped from 62 to 54 times a year, on average.

As an article published by UC Berkeley noted, however, a drop in sexual encounters from 62 to 54 times per year means that the average adult is still having sex more than once a week.

And as Cosmo pointed out, since the GSS doesn’t define “sex,” it’s hard to know if the respondents counted oral, mutual masturbation and non-penetrative into account when self-reporting on their sex lives.

5. Most of us are trying to date out of our league.

Swipe right, even if you’re doubtful that Chris Hemsworth lookalike will do the same for you. According to a study published in August 2018 in the journal Science Advances, users of online dating sites spend most of their time trying to contact people out of their league.

Researchers reviewed thousands of messages exchanged on an unnamed “popular, free online-dating service” between nearly 200,000 straight men and women.

After a month of careful observation, they found most online daters tend to message people exactly 25% more desirable than they are (with desirability determined by how many messages a user received during the month).

“Our study suggests that people are pursuing partners who are a little more desirable than they are. Women are a bit less aspirational than men,” Elizabeth Bruch, an associate professor of sociology at the University of Michigan and an author of the study, told HuffPost.

6. Men having affairs are more likely to break their penis.

Men, be wary of those 5 p.m.-to-7 p.m. relationships with someone who’s not your spouse: That casual affair might result in a fractured peen.

According to a 2011 study published in the Journal of Sexual Medicine, cheating may make a man more likely to suffer from penile fractures. Researchers at the University of Maryland Medical Center looked at men who “broke” their penises and found that half were having extramarital affairs at the time. (Relax, it’s not actually a break, it’s a rupturing of one of the tube-like chambers in the penis.)

What makes extramarital sex so risky? (Besides getting caught by your partner.)

“If a guy is having an extramarital affair or he’s rushed or in a weird place, the situation is different [somehow],” lead researcher Andrew Kramer told HuffPost at the time. “I think the time you don’t see a lot of men fracturing their penises is in the bedroom with his wife that he’s been married to for a number of years.”

7. If you want to get married, your best bet is to marry between the ages of 25 and 32.

Want to get married and stay that way? Don’t rush to get hitched when you’re young ― but don’t dawdle, either. Once you’re past your early 30s when you wed, the risk of a divorce down the road starts to creep up again, according to research that came out of the University of Utah in 2015.

Nicholas Wolfinger, a sociologist at the school, looked at data from the National Survey of Family Growth and found that while the risk of a marriage ending in divorce declines steadily as marital ages go from the teens into the late 20s, it then starts to rise again. Once you reach the age of 32 before getting married, the odds of getting a divorce once you do increase by 5%. In other words, the sweet spot to get married statistically speaking is from age 25 to 32. Some good general news about the state of marriage from the decade? The divorce rate is going down, partially because millennials are waiting to partner up ― or not partnering up at all. Hard to get divorced when you aren’t even getting married!

8. Divorce can be potentially deadly for men.

In the most Debbie Downer divorce research of the decade, researchers at the University of Nebraska found that divorced and unmarried men have higher rates of mortality and are more prone to substance abuse and depression than married men. The researchers also found that divorced men are more likely to partake in risky activities such as abusing alcohol and drugs, and divorced or separated men have a suicide rate that is 39% higher than that of married men. Depression is also more common for divorced men than married men, and divorced men undergo psychiatric care 10 times more often than married men do.

9. That sexual afterglow you feel after sex lasts 48 hours.

You’re generally in a better mood after sex, thanks to a flood of endorphins and other feel-good hormones released post-climax ― aka, sexual afterglow.

In 2017, researchers from Florida State University found that the positive effects of getting laid last up to two days ― and that the feeling can help couples bond over time.

Lead researcher Andrea Meltzer told HuffPost that there might be an evolutionary reason for the 48-hour shelf life.

“Forty-eight hours is roughly the same amount of time that (a) conception is maximized, (b) it takes sperm concentrations to be restored to peak levels, and (c) sperm remain maximally viable in the female reproductive tract,” she said. “It’s really interesting that lingering cognitive implications of sex ― sexual afterglow, for instance ― last for the same amount of time as the biological implications of sex.”

10. A close relationship with your in-laws may change your divorce odds.

Happy wife in-laws, happy life? In November 2012, a 26-year longitudinal study released by the University of Michigan found that when a husband reported having a close relationship with his wife’s parents, the couple’s risk of divorce decreased by 20%. On the other hand, when a wife reported having a close relationship with her husband’s parents, the couple’s risk of divorce increased by 20%. Why the difference?

Researcher Terry Orbuch told the Wall Street Journal that she believes that many wives eventually view their in-laws’ input as meddlesome, while husbands tend to take their in-laws’ actions less personally.

11. Couples who share chores have better sex lives.

Pitching housework to your partner seems supremely unsexy, right? Next time you do it, mention this study finding: In 2015, researchers from the University of Alberta found that couples who divvied up chores had higher relationship satisfaction and had more sex than couples who didn’t mutually contribute.

“A division of household labor perceived to be fair ensures that partners feel respected while carrying out the tasks of daily life,” lead researcher Matt Johnson wrote. “Completing housework may or may not be enjoyable, but knowing that a partner is pulling his weight prevents anger and bitterness, creating more fertile ground in which a (satisfying) sexual encounter may occur.”