The sexual integrity you have before marriage is the sexual integrity you have after marriage. Saying vows and signing a certificate doesn't change that. Many couples think wearing a grand outfit surrounded by their closest friends and spending thousands of dollars on that magical night will change everything. It will change the way he talks to me. It will change the way she spends money. It will change his commitments. It will change her religious preferences. It will change the heart of sexual purity. But, that is not the case.
Chris and I were shocked by the lack of sexual purity in our marriage, but we weren't shocked by our lack of integrity before marriage. We wanted to show each other grace because of the shame, so we ignored the fact that we had issues to deal with. So many couples find it acceptable to live how they choose before marriage because they think it will change after the vows.
In meeting with couples for premarital counseling, Chris and I have heard some mention past experiences as "a mistake" and certainly some with shame. There are some in rebellion who will not hear the counsel of waiting until after the wedding date. Still, there are some who have their virginity, but there is no purity of heart and mind. If you find it acceptable to have sex outside of marriage before marriage, what is keeping you from having sex outside of marriage after marriage?
A new situation or circumstance cannot change purity. Only the renewal of our hearts and minds.
Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is--his good, pleasing and perfect will. Romans 12:2