Biblical marriage is exclusively the union of one man with one woman.  This is God’s only prescribed design for marriage, and is sacred not only in its practice according to God’s plan and design, but also in its portrayal of the union between Christ and His church.  Genesis 2:18-25, Matthew 19:4-6, Ephesians 5:22-33.  God created mankind as male and female, both made in the image of God, with equal worth and with distinct roles.  Though sin has had its effect and consequences on the human race, God’s plan and design in His creation of two distinct and complementary genders determined at the birth  of an individual is to be honored and upheld according to His sovereign purpose. Genesis 1:26,27, 2:20-23, Matthew 19:4.   God’s design for sexual intimacy is for one man with one woman within the context of their marriage. God’s Word makes clear that adultery, fornication, homosexual behavior, bisexual behavior, bestiality, incest, and the use of pornography is considered sinful and contrary to the will of God.   Matthew 5:27-32, 15:18-20, Romans 1:15-32, 1 Corinthians 6:9,10, Galatians 5:19-21, 1 Timothy 1:8-11, Hebrews 13:4,  Jude 6,7.