Contrary to Mrs. Grundy, sex is not sin. Contrary to Hugh Hefner, it's not salvation either. Like nitroglycerin, it can be used either to blow up bridges or heal hearts.
At its roots, the hunger for food is the hunger for survival. At its roots the hunger to know a person sexually is the hunger to know and be known by that person humanly. Food without nourishment doesn't fill the bill for long, and neither does sex without humanness.
Adultery, promiscuity (either heterosexual or homosexual), masturbation-one appealing view is that anything goes as long as nobody gets hurt. The trouble is that human beings are so hopelessly psychosomatic in composition that whatever happens to the soma happens also to thepsyche, and vice versa.
Who is to say who gets hurt and who doesn't get hurt, and how? Maybe the injuries are all internal. Maybe it will be years before the X rays show up anything. Maybe the only person who gets hurt is you.
In practice Jesus was notoriously soft on sexual misbehavior. Some of his best friends were hustlers. He saved the woman taken in adultery from stoning. He didn't tell the woman at the well that she ought to marry the man she was living with. Possibly he found their fresh-faced sensualities closer to loving God and humanity than the thin-lipped pieties of the Pharisees. Certainly he shared the Old Testament view that the body in all its manifestations was basically good because a good God made it.
But he also had some hard words to say about lust (Matthew 5:27-28), and told the adulterous woman to go and sin no more. When the force of a person's sexuality is centrifugal, pushing further and further away as psyches the very ones being embraced as somas, this sexuality is of the Devil. When it is centripetal, it is of God.