God said it was not good that man should be alone in Genesis 2:18. God made this statement when man was in a state of innocence, before he had sinned against the Lord. Even in perfect environment, it is better for man to not be alone.
“Then the LORD God said, “It is not good for the man to be alone; I will make him a helper suitable for him.”“ (Genesis 2:18, NASB)
There was no “helper” found for Adam among the animal kingdom, so God found a helper for him of his own kind - homo sapiens. “Helper” is עזר (‛êzer) in the Hebrew and means a helper corresponding to him, a helper of the same species. Adam needed a wife. Adam’s relationship with God preceded his relationship with the woman. The first human relationship in all of history was marriage. Gen. 2:20.
"The man gave names to all the cattle, and to the birds of the sky, and to every beast of the field, but for Adam there was not found a helper suitable for him." (Genesis 2:20, NASB)
Man was formed from the dust (chemicals) of the earth, but woman was made from the man (Adam’s rib). When the deity of Jesus Christ brought the woman to Adam, He was performing the first marriage ceremony in history. God causing the woman to be brought to the man indicates divine delegation of authority to the husband over the wife.
God separated something from Adam - his rib. Man is now no longer complete in himself. There is always something missing and that missing something can only be supplied and provided by a woman. The man is never complete without the woman. The purpose of the woman is to complement (complete) the man and to fulfill him. The man is completed by having the woman.
Marriage was established in the garden of Eden during the first dispensation – the Age of the Gentiles. Marriage became a divine institution when Adam and the woman were married by God.
There was sex in marriage long before there were children. The principle of establishing a home, apart from in-laws, was given before in-laws ever existed. The omniscience of God saw one of the greatest problems in marriage - interference of in-laws. Of course young couples bring on this problem many times by depending upon parents for such things as money, babysitting, etc. Gen. 2:24.
"For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh." (Genesis 2:24, NASB)
There are three exceptions to marriage and are stated in Matthew 19:12. Otherwise, marriage is for the human race. The first exception is the congenital eunuch who is one who lacks the ordinary waves of libido at normal times in life. The second exception is for those who become eunuchs through emasculation. The third exception is for those operating under the law of supreme sacrifice and who chose to deny themselves marriage for a higher purpose, such as the Apostle Paul.
““For there are eunuchs who were born that way from their mother’s womb; and there are eunuchs who were made eunuchs by men; and there are also eunuchs who made themselves eunuchs for the sake of the kingdom of heaven. He who is able to accept this, let him accept it.”“ (Matthew 19:12, NASB)