My best friend is male and I want him to stand on my side during the ceremony. It does make a huge difference to me whether he stands on my side or my FI. My theory is this, while our siblings are becoming family to both of us during the ceremony and thus can be separated by gender just fine, my best friend is still MY best friend, and so I want him next to me on the most important day of my life. Also, the idea that a girl can only be close to other girls has always struck me as outdated and sexist. Does anyone know though if the Catholic Church lets you do this?