And part of that relationship is sexual. Remember, God is pro-sex. But He is pro-sex when sex is within the context of the marriage relationship. That is the message of the Seventh Commandment. You may say it another way.
Sex is for marriage, and only for marriage.
Sex is risky business. By it's very definition, it is one of the most intimate encounter two people can have. Because it is intimate, it places us in a very vulnerable situation. That is why God confines it to the committed covenant relationship of marriage. There, in the marriage relationship, trust can grow.