God created man male and female—Adam and Eve—and He made males and females different physically and distinct in their roles. Genesis 2:18 makes Eve’s role clear: “It is not good that the man should be alone; I will make him a helper fit for him.” Eve was from the bone and flesh of Adam, meaning she is equal in her standing before God and yet distinct from man (Galatians 3:28). But God gave Adam the authority not only to name the animals but also to name his wife, indicating that she does not share equal authority with her husband. In the Bible’s wording, she is his helper.
If God’s creation of Eve, a female, as a helper and companion for Adam, a male, is not clear enough to defend marriage as being reserved for a man and a woman, Genesis 2:24 clears up any confusion: "Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh."
From the very beginning of God’s Word, He makes no allowances for “alternative” lifestyles such as homosexuality, bestiality, polygamy, and so on.