Citation please. There have been long standing traditions of polygamous marriage in cultures ranging from the Egyptians to Chinese to Polynesians to Jews and various tribes throughout Africa. I am unaware of a single culture with long-standing traditions of gay marriage but I'm not an anthropologist so perhaps in South America or Eastern Africa? I know the Hawaiians tolerated mahus but I don't recall anything about acknowledging mahu marriage.
BTW, as far as the claims of a tradition of divorce go, Freakonomics said the divorce rate climb that started in the 50s and 60s started dropping in the 80s and is now at or below historic norms. Divorce was so UNtraditional that Henry VIII's fears for royal succession precipitated a schism in the Roman Catholic Church and gave birth to the Church of England so he could get an annulment (not divorce) and marry a more fertile (he hoped) woman.
I apologize in advance to all the liberals or edgy self-styled libertarians for bringing actual facts and history into the discussion.