Bible passages describing same-sex marriage:
There are none! You can scan from the beginning of Genesis to the end of Revelation, and not see even a single same-sex marriage mentioned.
The Bible does contain:
Three stories of loving, same-sex relationships in the Bible involving David, Ruth and Daniel. But there is no indication that any of the three involved sexual activity.
A dozen or so oft-quoted passages about homosexual behavior in the Bible. Because conservative and liberal Christians interpreted the Bible very differently, they reach totally different conclusions about their meaning: Many conservative Christians interpret these passages as stating unambiguously that all homosexual behavior is forbidden, is an abomination, and is hated by God. It does not matter whether it is in the form of casual sex with a stranger, or sex within a committed, monogamous relationship. It is all sinful. Some consider it an "ordinary" sin -- in the same league as all other incorrect behavior, like lying, cheating or stealing. Others consider it such a serious sin that it will prevent gays and lesbians from attaining Heaven after death, even if they had previously been saved.
Many liberal Christians largely ignore English translations of the Bible which are often heavily biased against homosexuality. They prefer to refer to the original Hebrew and Greek. They frequently interpret these passages as condemning: Homosexual rape (Genesis 19; Judges 19:14).
Homosexual ritual sex in Pagan temples -- a religious taboo (Leviticus 18:22 and Leviticus 20:13).
Homosexual prostitution (Deuteronomy 23:17; 1 Kings 14:24, 15:12, 22:46; 2 Kings 23:7).
Heterosexual men and women going against their basic nature and engaging in homosexual Pagan orgies (Romans 1:26).
Men who sexually molest boys -- and the boys that they abuse (1 Corinthians 6:9; 1 Timothy 1:9).
Bestiality: Men engaging in sex with males of another species -- angels in this case (Jude 7).
But on the topic of sexual activity within a loving, committed, monogamous homosexual relationship, many religious liberals view the Bible as being completely silent.
One of the very few beliefs on which conservative and liberal Christians agree is that there are no definitive statements in the Bible which deal directly with same-sex marriages (aka domestic partnerships, civil unions, holy unions, etc.)
The books in the Christian Scriptures were all written before 100 CE (according to most conservative Christians) or 150 CE (according to most liberal Christians). The concept of homosexuality as a sexual orientation that could lead to a committed, long term relationship was not developed until the late 19th century. Thus, one can not expect to find biblical references to same-sex marriage. There are no references to planes, trains or automobiles, either.
There are two sources that we can use to infer Christian perspectives on same-sex marriage:
Bible passages which deal with principles of love, sex, and marriage. Conservative and liberal approaches are described below. They come to opposite conclusions.
Direct assessment of the will of God through prayer. Unfortunately, according to a pilot study of some visitors to this web site, this path does not seem to be available.