While I fail to see why a character's sexuality has any bearing, I'm not opposed to having them. Could easily slip in during some of the npc filled side-quests or spurts in the MSQ. Not out the ordinary for one person in a couple to be able-bodied for combat and the other is not in XIV's world. An npc could easily mention that their spouse is part of X group of guards/recruits/laborers/etc that the PC is currently looking for. Or even have some nameless npcs in a town or so holding hands, hugging, etc.

Don't need to have the sexuality blasted. There are ways they could slip it in tastefully.