There are 2 real good books I think you would love on this subject. Sex At Dawn by Christopher Ryan and Cacilda Jetha. And also Gender by Ivan Illich. I know in North America 'Turtle Island' The Native Americans, have the 3 genders as well. People who are attracted to the same sex in Native culture are known as 2 spirited people. https://en.wikipedia.org/wiki/Two-Spirit

I think there is a difference with identifying with the opposite gender and sexual or passionate relations with someone of the same sex. Although of course, the 2 can go together and often do.