1 Corinthians 7:1-24

Paul's instructions on sex and marriage were that married couples have a responsibility, one to the other to ensure that sexual satisfaction is found in the marriage bed so that there is no temptation to indulge in extramarital relations. It is not better or worse to be married or single, but if you choose to be single, you must remain celibate. If sexual temptations are such that you can't remain celibate, get married so as not to be tortured. If you find yourself as a Christian living with an unbelieving spouse, don't leave them. As long as they are willing to remain married, you should too. Your influence may be what leads them to the Lord. If the unbelieving spouse wants to divorce, they should be allowed to go.

Simply put, sex belongs within the confines of marriage. Any sexual relations with someone other than your spouse constitutes sin in God's eyes. The marriage bond is sacred. Once you enter into a marriage, you are committed for life. If you become a believer after you marry, that is no reason to dissolve the marriage. It does not change the definition of marriage or absolve you from your commitment. Quite the opposite, you now have a commitment to pray for your unsaved spouse and witness to them in the hopes that one day they will gain salvation as well.