I've got a very nice cave with an excellent T1 connection. From this cave, I have certainly learned about a number of ancient Greek city-states that sanctioned and institutionalized, at various times, homosexual relationships. However, almost all of them were based on pedophilia, and relationships between two post-pubescent males were generally frowned upon. At least according to the limited sources we have available. How do you suppose this would play in a court of law considering the historical precedents for same-sex marriage?
There are also some interesting records concerning the early Christian church, describing sanctioned same-sex unions, primarily between clergy. Of course, the primary inheritor of this tradition is the Catholic church, which almost certainly has, for a period of time perhaps most properly described as centuries, been the single most active organization in the world behind the sexual molestation of minor boys. So... records are there, but not particularly helpful.
A number of Native American tribes, I understand, did practice some degree of same-sex union, but, as I understand it, such unions were almost always based on one partner being a highly effeminate male, and this effeminate male assumed the role of 'wife' in the relationship.
There are other records also, you are right. What I stated about there being no historical record that enabled homosexuals to marry each other is wrong, and I apologize for the error. However, the practices were almost universally abandoned and generally condemned after a few centuries in most civilizations where they were, for a time, present. Not really the best precedent, again, for a court of law considering the specific question of declaring states' bans on same-sex marriage unconstitutional throughout the United States.