I have to agree with Theodric here - it's not really something the development team is going to specifically refer to (because doing so risks a review of the game's classification which allows more younger players and thus more players period). Of course there are obvious innuendos, sexual references and statements made about Eorzeans' sexuality, but it's not something that is going to be outright stated in a lore post, unless it's done in a more subtle way (such as how Ferne's thread about Humbert Longhaft and all the inneundos about 'his lever').
However, that does not mean we don't know at least a little about Eorzea's sexual situation. Eorzeans seem to be very open and egalitarian about their sexuality, long standing social taboos and moral questions about sexuality in our world seem to not exist (or if they do, they're more downplayed). The Ceremony of Eternal Bonding is an example of this, ceremonies regard those participating as equals regards of their gender, and it's taken as a normal thing (same sex marriage is even referred to by npcs - back during the first Rising event the (female) vendor stated if asked about her outfit stated "her wife" made it for her, and the context is made as no big deal. It's something that is just taken for granted.
Even gender roles are blurred - the three main citystates all have women as their official head of state, women can take up a sword or wand and serve as a soldier or adventurer just as much as pursuing more 'traditional' roles such as raising a family or 'keeping house', and again it's taken as socially normal. And many npcs are outright open about their sexuality, a good example is Momodi, she is well known for 'comparing manhoods' and swooning over attractive men like Thancred (as she did in 1.0).
Either way, Eorzea is a very open place sexually. It's not "drowning in sin" as those of more self-proclaimed moral character might state, but they're definitely not prudes by any stretch.