Shacking up isn't the same. Matthew 19:4-6

"Have you not read that he who created them from the beginning made them male and female, and said, Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh? So they are no longer two but one flesh. What, therefore, God has joined together, let not man separate."

This is not the first time we have seen statistics like this: Cohabiting couples were nearly eight times more likely to separate due to discord than married couples in the first year of a relationship. Cohabiting couples were nearly four times more likely to separate in the second year, and three times more likely to separate in the third year. Cohabiting couples had a separation rate five times that of married couples, and following separation, cohabiting couples had a rate of reconciliation that was one-third that of married couples.

Unfortunately, too many people try to tell us it's OK. More unfortunately, too many people in our churches try to justify it too. Get it right: Shacking up is not the same as marriage. If you shack up before you get married, you are far more likely to end your relationship in divorce.

I first read about this in a "Marriage and Family" class at Illinois Central College, part of the sociology curriculum there. I should note that that class clearly was very liberal, and that the data below is coming from the Heritage Foundation, which is on the other side of the political spectrum.
That said, the numbers come out the same.

Cohabitation is not the same as marriage. It doesn't help couples improve their marriages. Cohabiting couples report poorer relationship quality and well being. Cohabiting relationships and even subsequent marriage tend to be less enduring.

Cohabiting couples are more likely to separate and less likely to reconcile after a separation than married couples. Read these sobering facts. Read the full report here

• Cohabiting couples are more likely to experience infidelity than married couples. 
• Compared to women who did not cohabit before marriage, those who did are more likely to experience divorce or separation. 
• Cohabiting couples without plans to marry tend to report poorer relationship quality than married couples. 
• Among individuals in their fifties, those who are cohabiting tend to have accumulated less wealth than their married peers. 
• Among mothers with infants, those in cohabiting relationships tend to fare worse economically than married mothers. 
• Men in cohabiting households tend to have lower earnings than married men with families. 
• Compared to their married peers, women who are cohabiting tend to have higher earnings relative to their partners’ earnings. 
• Compared to married individuals, those who are cohabiting tend to report higher levels of depression. 
• Individuals who are cohabiting report, on average, more alcohol problems than married individuals.

There is a reason why God said don't do it. It's called sin. And there is only one cure from it: Turn! Turn and repent! Confess your sins. Repent. And turn to God, who will restore you.