I am of the age and generation where many of my friends are cohabiting with significant others before marriage. Not coincidentally, many from my generation grew up with divorced parents or with other “modern family” permutations. When we discuss the advantages of cohabitation before marriage, many twenty-somethings believe living with their partner before getting married will help them avoid their parents’ (or friends’ parents’) divorce pitfalls. Nonetheless, studies show that couples who live together before getting married are more likely to divorce (although the association seems to be weakening). Clearly, one must distinguish correlation and causation: living with someone before marrying them does not cause divorce. Other factors are at play.
Often what makes the difference in marriage success for couples who choose to cohabit is how and why couples find themselves cohabiting. For many, cohabitation is something that just happens: her lease is up, she has been dating someone she likes, maybe loves, for eight months and things are going well. Rent is really expensive and they spend most nights together anyway – why not? The “why not?” attitude, often without a conversation regarding the future or what moving in together means, is associated with the concept of “drifting.” Drifting is described as sliding from living together into getting married without really thinking about it. It seems logical that when couples slide from dating to living together, they might also slide from living together to marrying without stopping to think. Without thoughtful deliberation about whether this person is someone you should be marrying, it is understandable that couples who drift into marriage do not last. For young couples cohabiting and concerned about getting divorced, it is advisable to assess the relationship and really think about marriage before sliding right into it. Breaking up a marriage is often more complicated, expensive, and painful than deciding as an unmarried couple to split up, if for no other reason than the legal hurdles and ramifications; it is an institution that should be entered thoughtfully.
Conversely, I have many friends living with their boyfriend or girlfriend who talked about wanting to commit to each other for life, planning to be married someday, before deciding to move in together. They may talk about their hopes and dreams, whether they want kids and how many, where they want to live as a family, all before deciding to move in together. My guess is that a study distinguishing between couples like this compared with drifters would show that the former are not as likely to divorce. Couples who choose to move in together as a conscious step toward getting married or after getting engaged do not have divorce rates different from couples who do not move in together until after getting married. Ultimately, young couples who wish to cohabit should not fear that it will make them more likely to divorce if they take the time to think about whether the potential cohabiter is someone they someday plan to marry.
 Scott M. Stanley & Galena K. Rhoades, “The Timing of Cohabitation and Engagement: Impact on First and Second Marriages.