A fascinating piece of history from the long battle for marriage equality:
In the period up to roughly the thirteenth century, male bonding ceremonies were performed in churches all over the Mediterranean. These unions were sanctified by priests with many of the same prayers and rituals used to join men and women in marriage. The ceremonies stressed love and personal commitment over procreation, but surely not everyone was fooled. Couples who joined themselves in such rituals most likely had sex as much (or as little) as their heterosexual counterparts. In any event, the close association of male bonding ceremonies with forbidden sex eventually became too much to overlook as ever more severe sodomy laws were put into place.
Such same-sex unions—sometimes called “spiritual brotherhoods”—forged irrevocable bonds between the men involved. Often they involved missionaries about to set off on foreign voyages, but lay male couples also entered into them. Other than the gender of the participants, it was difficult to distinguish the ceremonies from typical marriages. Twelfth-century liturgies for same-sex unions, for example, involved the pair joining their right hands at the altar, the recital of marriage prayers, and a ceremonial kiss.
Another excerpt from Sex and Punishment: Four Thousand Years of Judging Desire, by Eric Berkowitz, covers the history of lesbian relationships.