Marriage is the moral context for sex. Safe sex is moral sex. Marriage was instituted in Creation. God created man male and female commanding them to be fruitful and multiply. Marriage was given to provide companionship, as the context for sex and procreation, and to be the nucleus of social order.
Marriage is inherently a sexual relationship in that it is the union of the two sexes.
Those who view God as being somehow against sex are mistaken. Adam and Eve were made to have sex. But sex, due to sin, has become another arena in which man's rebellion against God is demonstrated. Sex is not sinful, but God judges sinful sex. Jesus says our sexuality involves more than our genitals, that even to look at a woman with lust is to violate the seventh commandment.