Breakpoint, Christianity Today, and the Institute for Family Studies recently reported on a new Pew Research survey indicating that American evangelicals embrace premarital sex and cohabitation in increasing numbers. Writing for IFS, David J. Ayers says, “It is stunning that this has quietly come to pass among adherents to a form of Christianity that emphasizes radical obedience to an inerrant Bible, forbids all sex outside marriage, and emphasizes being distinct from “the world.”
You can read the research using the links above. But more is at stake than who is shacking up and who is not. As Ayers mentions, the first issue for Christians is obedience to Christ. We want that to be enough, but experience tells us that it helps to have other reasons to support our choices. As a marriage counselor for 25 years, I can tell you that the most potent reasons have to do with negative relationship dynamics set in motion with premarital sex and cohabitation.
In his 2011 book, The Ring Makes All the Difference, Glenn Stanton cites five reasons everyone, not just Christians, should consider.
- Marriage matters, not just because it is preceded by a wedding that costs tens of thousands of dollars, but because the nature of the relationship itself makes a difference in ways you probably never imagined. Bottom line: A solemn vow made before a supportive community is a surer foundation than economic convenience and sexual passion any day.
- Even if (cohabiting) couples consider themselves essentially “married,” they know that they are freer to exit the relationship at any time without a marriage license. This lack of security in the mind of each partner affects how they deal with each other before the wedding and unconsciously carries over later.
- Marriage involves things the cohabiting couple–or at least one of them–would rather not address. Financial values, child-rearing values, and relational exclusivity—that part about “forsaking all others”—are among them.
- People with cohabiting experience who marry have a 50 to 80 percent higher likelihood of divorcing than married couples who never cohabited. Those conclusions are disputed but dig down in the data, and you will find enough reason to push pause on cohabitation.
- All of those findings are important, but the one that stood out most, because it is the one that I deal with most often in counseling, is that cohabitation–even with someone you eventually wed– sets up unhealthy relationship patterns that carry over into the marriage. Cohabitors have fewer and weaker conflict resolution skills. They are less likely to be supportive and self-sacrificing. Most notably, “the lack of relational clarity is likely to foster more controlling and manipulative interactions to try to keep the relationship together and get the partner to do what the other desires. As a result, cohabitors are much more likely to report a sense of relational instability than their married peers.”
No wonder the Apostle Paul warned us about wronging each other in these matters.
For you know what instructions we gave you through the Lord Jesus. 3 For this is the will of God, your sanctification: that you abstain from sexual immorality; 4 that each one of you know how to control his own body in holiness and honor, 5 not in the passion of lust like the Gentiles who do not know God; 6 that no one transgress and wrong his brother in this matter, because the Lord is an avenger in all these things, as we told you beforehand and solemnly warned you. 7 For God has not called us for impurity, but in holiness. 8 Therefore whoever disregards this, disregards not man but God, who gives his Holy Spirit to you. 
 Glenn T. Stanton’s The Ring Makes All the Difference: The Hidden Consequences of Cohabitation and the Strong Benefits of Marriage.