With the romantic haze of Valentine’s Day behind us, can we return to the reality of relations between the sexes?

Start with a new film short, “The Economics of Sex,” from the Austin Institute for the Study of Family and Culture. The think tank’s “whiteboard video” — the kind where someone is drawing really fast — should be mandatory viewing for every woman between the ages of, say, 16 and 40.

The economics of sex isn’t a new topic and has nothing to do with anything illegal. It’s the study of where the supply and demand curves for sex meet.

The nice thing about viewing sex in economic terms is that we don’t have to satisfy the goddesses of political correctness. Here’s how the video lays things out:

“On average, men have a higher sex drive than women. Blame it on testosterone, call it whatever you want — but on average, men initiate sex more than women, they’re more sexually permissive than women, and they connect sex to romance less often than women.

“Nobody’s saying this is the way it ought to be. It’s just the way it is.”

“Women, on the other hand, are likely to have sex for reasons beyond just simple pleasure. Her motivations for sex often include expressing and receiving love, strengthening commitment, affirming desirability, and relationship security.”

How refreshingly honest — in a way that parents of adolescent girls should appreciate. These moms and dads don’t have an easy task: Though they know (and the research confirms) that their daughters will be happier if they delay sex until at least 17 or 18 and limit the number of partners they have, these girls are surrounded by cultures that offer a different message. Pop culture says everyone around you is enjoying casual sex; elite culture insists that women and men are exactly the same in this regard.

Most parents, even moderately religious ones, don’t feel comfortable telling their daughters not to have premarital sex because of divine retribution anymore.

“I don’t flat-out say, ‘Wait to get married,’ like my mother did,” one Catholic mother of a 14-year-old in Scarsdale tells me. She advises her daughter to “not give herself away easily or too many times” and that “sex is better when you are married and in love, so waiting is always better.” She wonders, “Does that sound conflicting and-or confusing? Maybe a tad bit, eh?”

When her son and two daughters were growing up in Park Slope, Kay Hymowitz says she never had an explicit discussion with them about avoiding casual sex or delaying sex in general; “They just knew.” But one reason they just knew, says Hymowitz, a Manhattan Institute scholar, is that they had “quasi-psychological” discussions at the dinner table, which included “why boys seemed one way and girls another.”

What many parents never get to, but should, is the next part of the video, which asks: “So in an exchange relationship where men want sex more often than women do, who decides when it will happen?” The answer: “She does, of course. Sex is her resource. Sex in consensual relationships will happen when women want it to.”

It is safe to say that few teen girls, let alone 25-year-old women, understand the truth of that statement, or its significant implications. They feel pressure coming at them from all sides to have sex early and often — even though, ultimately, they hold all the cards.

Or at least they could. And this is where the economics matters. Because many more women than men are in the market for a serious relationship, the video explains, “men can be picky and can insist on extensive sexual experience before committing.” Women’s competition for those men has increased, and so the “price” of sex — what the man has to “deliver,” emotionally and commitment-wise — has gone down.

If girls did actually come to realize that they’re “in the driver’s seat” when it comes to sex (and if sisterhood really were powerful), they could change the market entirely, having sex only when they were ready and only when they saw a serious commitment on the part of their partner.

As the voiceover in the video explains, “Collusion — women working together — would be the most rational way to elevate the ‘market value’ of sex.”

Call it the OPEC of sex. If this collusion worked, we’d see “on average more impressive wooing efforts, greater male investment, longer relationships, fewer premarital partners, shorter cohabitations and more marrying going on.”

Well, by next Valentine’s Day . . .