The Census reports a 72% increase in the number of cohabiting couples since 1990. Unfortunately, research shows that cohabitation is correlated with greater likelihood of unhappiness, and domestic violence in the relationship. Cohabiting couple report lower levels of satisfaction in the relationship than married couples. Women are more likely to be abused by a cohabiting boyfriend than a husband. Children are more likely to abused by their mothers’ boyfriends than by her husband, even if the boyfriend is their biological father. If a cohabiting couple ultimately marries, they tend to report lower levels of marital satisfaction and a higher propensity to divorce.

Recent reports and commentaries on cohabitation tend to downplay these difficulties. I suspect this is because people do not know how to make sense of the research findings. Many people imagine that living together before marriage resembles taking a car for a test drive. The "trial period" gives people a chance to discover whether they are compatible. This analogy seems so compelling that people are unable to interpret the mountains of data to the contrary.

Here’s the problem with the car analogy: the car doesn’t have hurt feelings if the driver dumps it back at the used car lot and decides not to buy it. The analogy works great if you picture yourself as the driver. It stinks if you picture yourself as the car.

The contract or consent approach doesn’t really help much either. Living together is fine as long as both people agree to it. The agreement amounts to this: "I am willing to let you use me as if I were a commodity, as long as you allow me to treat you as if you were a commodity." But this is a bogus agreement. We can say at the outset that we agree to be the "man of steel", but no one can credibly promise to have no feelings of remorse if the relationship fails.

All of this points to the essential difference between sexual activity and other forms of activity. Giving oneself to a sexual partner is, by its nature, a gift of oneself to another person. We all have a deep longing to be cherished by the person we have sex with. That longing is not fooled by our pretensions to sophistication.

Here is an analogy that works better than the taking the car for a test drive analogy. Suppose I ask you to give me a blank check, signed and ready to cash. All I have to do is fill in the amount. Most people would be unlikely to do this. You would be more likely to do it, if you snuck out and drained the money out of your account before you gave me the check. Or, you could give me the check and just be scared and worried about what I might do.

Think about it: What do you have in your checking account that is more valuable than what you give to a sexual partner? When people live together, and sleep together, without marriage, they put themselves in a position that is similar to the person being asked to give a blank check. They either hold back on their partner by not giving the full self in the sexual act and in their shared lives together. Or, they feel scared a lot of the time, wondering whether their partner will somehow take advantage of their vulnerability.

No one can simulate self-giving. Half a commitment is no commitment. Cohabiting couples are likely to have one foot out the door, throughout the relationship. The members of a cohabiting couple practice holding back on one another. They rehearse not trusting. The social scientists that gather the data do not have an easy way to measure this kind of dynamic inside the relationship.

In my view, this accounts for the disappointing results of cohabitation. I am sorry to say that I learned this from experience. My husband and I lived together before we were married. It took us a long time to unlearn the habits of the heart that we built up during those cohabiting years.

The sexual revolution promised a humane and realistic approach to human sexuality. Ironically, the uncommitted-sex mentality has proven to underestimate both the value and the power of sexual activity. Lifelong, committed marriages are difficult, no doubt about it. But self-giving loving relationships still have the best chance of making us happy.