There is evidence of the Ming Dynasty having elaborated rituals in which females would enter a marital contract with younger females, and males would enter similar institutions with males (and you thought modern gender norms for jobs like maids and secretaries were bad?). These contracts were entered into with the permission of the king and the subjects, especially in the province of Fujian province, and marriages of the same kind with startling similarities to Chinese weddings were followed in the Eastern most parts of Europe.
Even the Zhou dynasty period of China has recorded evidence of the Pan Zhang and Wang Zhongxian, who entered male domestic partnership, and was compared to heterosexual marriage. However there were no rituals surrounding these arrangements whatsoever. This reflects deeply how far back the acceptance of same sex union goes to. It should be kept in mind that these were ancient civilizations and had very strict laws and rules which were upheld in the highest honors, both for inside the home and outside. There were no tolerances for any kind of democracy and voicing of opinions, as compared to the present. However, these dynasties and civilizations were still tolerant of the entire basis of same sex unions and not only did they allow them, they documented them as well, and celebrated them with pomp and ceremony.
Even if we consider the western hemisphere, we can see some Western societies that integrated same sex unions into their systems. The ancient Greeks had pederasty as a form of union for most of the same sex love cases, and on the most part it co existed with the institution of marriage. Documented cases in this religion claimed these unions to be temporary and pederastic. However, at this time unions like these created Moral dilemmas for the Greeks and were not universally accepted.
Even the Romans documented some cases of same sex unions to be performed, as provided with evidence by emperors Nero who married a young boy and the child emperor Elagabalus who both supposedly married a man, and by its outlaw by the Christian emperors Constantius II and the Constans in 342 AD but the exact intent of the law and its relation to social practice is quite unclear with only a few examples of same sex marriage in the culture exist as well.
Christian Church and the policy of the Middle Ages, however, brought in an era of non tolerance to same sex marriages as they were seen as a violation to the Bible and its teachings as well as the teachings of Talmud and Torah, which did not allow the practices as they were seen as a contradiction to the nature of reproduction and the will of the creator (many today still believe this). Hence it was viewed as a Moral shortcoming. Even after the Theodosian code passing the Christian Emperors continued to collect taxes on male prostitutes until the reign of Anastasius.
In the years 390, the Christian emperors declared homosexual sex to be illegal and forbidden for those who were guilty. The Christian emperor Justinian made homosexuals a blaming point for all the problems such as famine, earthquakes and pestiliences. It was nonetheless controversial even though there was an era of tolerance in pre-Christian Rome.
In this way homosexuality was preached and spread in different ways throughout the centuries.