For the most part...there is no indication for most NPCs what their sexual orientation is, since that has no real bearing on the story. Yes, there is that NPC pair from the Wanderer's Palace HM side-story (who were, incidentally, prosecuted more because they were interracial than gay), and the two in the Whitebrim barracks. And yes, Haurcefaunt, who is most likely bi.

Its just not important. Unless its stated otherwise, any NPC could be any orientation; we just don't know, because it (usually) doesn't matter in the setting.