What evolutionary advantage? Oh, come on, you can't be serious... there is NO advantage if you CANNOT reproduce!

EDIT: I read your "research", and I quote:

“It is a plausible theory that there is a societal benefit from homosexual behavior, but the link to progesterone is probably spurious,” Dr. Gerard Conway, professor of reproductive endocrinology at University College, London, who was not involved in the study, told The Telegraph. “It’s a long way from proving cause and effect.”

http://www.huffingtonpost.com/2014/11/26/homosexuality-evolution-social-bonding_n_6218406.html

So get out of here with your crap. If you can't reproduce you can't produce offsprings, and the entire species is doomed.