The reason why the game make you exited by woman, even if you're gay, is to balance the sexualities, otherwise a straight man could arouse everyone and being immune to nearly all the enemies, while a bi man could be aroused by everyone and not be able to arouse everyone.
By the way you talk about this problem, it makes me think that you've not played the game enough. The function of sexualities is to change the rate of female/male enemies that you can encounter, so if your character is gay you'll never meet the female bandit or the female harpy, and the only unavoidable female enemies that could arouse you will be the nymph and the lizardman acolyte. Only two among more than 40 types of enemies. Plus, if you don't want to be aroused by the nymph, you can use the hate potions so their attitude will fall and they will attack instead of flirt.
You say that gay shouldn't even be an option, if your character is going to be bi anyways, but, actually, the main character turns gay if you don't lock your orientation, since there are more men to seduce in combat than women and by game mechanic this change your sexuality from bi to gay. In all the game there are more or less a dozen sex scenes with women, while there are more or less two hundred with man, plus in all the game you can see only two images of naked women, while naked men are abundant. You're focusing on two/three scenes in the early game that involve women, but if you'd continued the game, even playing as a bi character, you'd see that horny women are practically non existant.
In my opinion, it's paradoxical that you say that the game is not meant for you, a gay man, and that is meant for bi folks, when in reality bi folks are complaining that there are not enough sex scenes involving women and say that this is a gay game with just a sprinkle of straight sex, just so it could seem to be bi.
My advice for you is to continue playing the game, you'll realise that this is not a game where your sexuality is basically implied just not to exist. Or don't. Playing this game, unlike your sexuality, is a choice. XD