If you're going to go by game lore, well, I suspect places like San d'Oria wouldn't be in support of gay marriage, so you wouldn't get married in San d'Oria, but maybe you should in Windurst who seem a lot more laid back. But it's a fantasy game, sure it takes inspiration from History and the mythology and religions of several different cultures, it doesn't mean there's any kind of Historical accuracy to it. Heck the game constantly breaks consistency for features, so why would it really matter?
And I think as marriage has been added for kicks and fun there's no reason there should be any restrictions on which players want to pair up. As said, it's not real marriage. If somebody would rather go for the proper thing in the game for the little 'M' above their head, then let them, after all, those two cat ladies could be a manthra and his girlfriend, so it's not just homosexual marriages being prevented (heck a manthra could easily marry his hume M boyfriend, so really gay players can have their marriages).
