What does sexual purity mean exactly?
Sexual purity includes abstaining from intercourse until marriage, but that is not all it means. Jesus said, "You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart" (Matthew 5:27-28). By Jesus' definition, being sexually pure means not even dwelling on thoughts of sex with someone other than a spouse.
Until you are married, sexual purity means saying no to sexual intercourse, oral sex, and even sexual touching. It means saying no to a physical relationship that causes you to be "turned on" sexually. It means not looking at pornography or pictures that feed sexual thoughts.
Sexual purity does not end with marriage. Marriage partners are supposed to experience sexual love with each other in a way that is fulfilling to both. However, purity means being completely faithful to your spouse in thought and deed. "Marriage should be honored by all, and the marriage bed kept pure, for God will judge the adulterer and all the sexually immoral" (Heb. 13:4).
Is sex a bad thing?
No. God designed us as sexual beings. He invented sex! He also made a place for it--marriage. In Genesis 2:24 God tells of His plan for marriage, that "a man will leave his father and mother and be united to his wife, and they will become one flesh." The sexual relationship makes the two become one flesh. The Bible speaks of sexual immorality, so there must also be such a thing as sexual morality, right? That morality is based on God's plan for sex.
If we're in love, isn't it OK?
God created sex for a lifetime commitment between one woman and one man. Sex outside of a committed marriage relationship violates God's standards. When you are wearing a wedding ring, you won't have to hope your partner loves you; you will have heard your spouse pledge to you in front of God, your families, and your friends. Anything less cheapens sex.
What if things just happen?
Sex is not an accident. Sex is progressive, meaning one act leads to another. Things won't "just happen" if you set boundaries and stick to them. If you make the decision now to abstain from sex and to live a pure life, then you will already know the answer before you encounter any compromising situation. Plus, the Holy Spirit gives us self-control to use when we are tempted.