In fact, the Apostle Paul says not to deprive each other of sex. False teaching says sex is dirty. Abuse of sex leads to dirty things. Christians have no reason to feel any shame about sex within their marital bonds. I realize how much this goes against popular thinking.
Sex is for marriage, period.
In any other context or relationship, it is more harmful than helpful. Sex is somewhat like fire - it has great power. In the right place and right time, used right way, it is constructive, pleasurable, and wonderful. But outside of its proper boundaries it can cut loose with an amazingly destructive force. Sex is God's glue for marriage.