Is that right? I never heard about this, how did this "brother-making" ceremony worked and what are good examples of this?
"Brother-making", or Adelphopoiesis, was a common practice in Medieval Byzantium and I've read a book by Claudia Rapp that listed an insanely high number of such rituals in Europe, after the Byzantine refugees came to France and Italy, where they provoked the Renaissance (pardon me, but one of the most, er... "fabulous" period in history. Tully, for example, received such union at some point, and everyone in the Versaille court knew that he was bisexual.). The thing is : there has been a massive drop in charges of sodomy after the Byzantines brought the ritual in Europe, because legally, you couldn't accuse someone of breaking a holy vow like that, which was very convenient (yes, it's supposed to be chaste. Platonism too is supposed to be chaste, and we all know what was going on between the tutor and the youngun. It's supposed, just like you're supposed to not lie when you declare your earnings.). You could only nullify it if the couple demanded it, which created a legal loop. They swore a vow of chastity, so they were legally protected. You couldn't accuse them of breaking the said vow, and you couldn't conduct an investigation as easily as before. As said, the charges of sodomy dropped massively after the ritual was introduced in Europe.
Adelphopoiesis existed under Augustus already, and he had a problem with his population because of it. Apparently, more than half of the population didn't reproduce and people everywhere were having Adelphopoiesis rituals. He had to create a baby bonus for the people to start making children again, and Adelphopoiesis was already supposed to be a friendship binding, not a gay union. Legally, it doesn't prevent someone from making babies with his wife, but in reality, the link was pretty obvious.
Back to the medieval Europe : the crusaders, and more precisely the templars, travelled with Byzantine military orders in which Adelphopoiesis was common (Many priests, and even st Thomas of Aquins have raised concerns about how common homosexuality was in the military orders), and these templars came back with what they called affrerement. The same order which has found itself accused of sodomy, and three different investigations, led by two actual popes (who, unlike King Philippe, didn't want the templars to be found guilty) all found proofs of the accusation.
Extremely popular within the borders with the Holy Empire too. For example, I've read in the "bibliothèque humaniste de Selestat" that in my village, called Scherwiller, there has been a problem with that, the priest made so many affrerement that the duke of Lorraine, a guy named Antoine, asked him for a report, and it turns out that every single couple bind by the affrerement was also declared sterile, so that people wouldn't ask questions about why they don't marry with women. And apparently, the Duke had demanded reports from all over the borders with the holy empire, which could indicate that it was a very common practice for legally protecting gay couples.