nobody has touched on this reason, the basic reason why all sin is wrong and is prohibited by our loving Creator God. Sin does damage, first to the individual. Sexual sin is the worst because sex is so integral to one’s identity that the injury to self is severe. Sexual sin with another person compounds the evil by the damage done to another. Sin that denigrates marriage - and the purpose of sex in marriage is 3-fold, unitive, procreative and pleasurable. Sex in marriage is a sign, as all the best of God’s gifts in creation, of His love, a sign of our potential union with God, a sign of His gift of life and a sign of the joy that awaits us in heaven. Anything that denigrates the sign value denigrates what the sign points to. Anything that denigrates marriage destroys the entire fabric of marriage and family, the basic construct of society. Sex before marriage destroys intimacy and destroys the process by which first in dating, courtship and then engagement the couple grow in intimacy. Sex shortcuts the whole process, so that intimacay of mind, heart, intention, purpose, faith never have a chance to grow. There has never developed any avenue of communication except sexual expression, women and men both are feeling used, a feeling compounded if they contracepted. This leads to bitterness, divorce and worse.
Listen to the wisdom of your elders, those of us survivors of the sexual revolution who have learned the truth to our cost. There is a reason why marriages among “good Christians” of 30-40 years duration are breaking up at a great rate. When sex is no longer possible or important, those relationships whose only basis was sex dissolve.
Marriage requires maturity. Inability to practice continence, which will be required for all at different times during marriage, and inability to subordinate one’s own physical needs and desires for the good of the other person and of the family, is the hallmark of immaturity and proof positive you are not ready for marriage.