The MC is not straight unless you play him as such - there are possible LGBT partners implemented already. There isn't a "gay" option to tick or anything like that, but you can choose to date solely men or women, nothing in game is forcing you into pursuing straight relationships.
Uh??? Yes it is forcing me??? Constantly? It's being shoved in my face at every single fucking turn without making any choices???
MC is aroused by every single woman in the game without fail and zero of the men. All of the flavor text points to interest in women. None of it points to interest in men. All the porn is straight porn.
Do you not know what LGBT means or something? Being a gay man does not mean "a man who only dates men." It means "a man who is only sexually or romantically attracted to men." A gay man would not be fucking aroused by every woman around him and none of the the men. That is not how sexuality works. What, do you think gay men go around saying "Wow, that woman is really attractive! I'm gonna ignore that fact and go date someone else I'm not attracted to."?
1) Calm down, man.
2) LGBT or Queer don't equal "a gay man" - the game includes gay, lesbian and bisexual characters already, and you (the MC) can choose to date whomever you want. Just because the flavour for the starting events, which are meant to showcase how certain mechanics work, is centred around the MC around women, you meet a potential gay love interest literally the first day of university as your guide.
3) Added to that, all the starting events that "skew" towards attraction to women are skippable - you can avoid Dee by not raising the relationship too high, Hinata by literally clicking "skip" and Ms. Madison by not accepting her quest - for the sake of allowing the MC to be roleplayed as a completely gay character.
4) Certain events later in game have the MC put into being very much aroused by not the opposite sex.
5) Even if the MC shows occasional attraction that isn't consistent with completely "straight" or "gay" orientation, the game still includes and explores the themes and includes characters that fit those categories, plus many more. There is a reason why it's in "LGBT" and "Queer" categories, not in a "Gay Main Character" category.
If you intended for "all the starting events that "skew" towards attraction to women" to be skippable, the game is bugged, because most of them absolutely are not skippable in any way. Meeting all the teachers, who are all female, is required and the MC is attracted to every single one of them without any player choice.
Furthermore, loving your mother in a familial way and wanting to do the tutorial to learn how the game works do not in any way imply that my character is attracted to women, except the game absolutely assumes I am if I make those choices. In fact, it assumes I'm attracted to Hinata before I make a single choice in regard to her.
Either you are still very, very, very confused about what sexuality is, or you have not playtested your own game. Given the fact that you keep going on about dating as if that has the slightest relevance to sexuality -- which it does not -- I assume it's the former.
It's possible that a heterosexual person playing this game wouldn't notice how completely in your face the MC's obvious heterosexuality is, but as a gay man myself attempting to play it, it could not possibly be more obvious without stating it explicitly.