Ohh yees this is a very, very excellent question Ethan ohhh :>c
I do not have their sexualities change depending on the scenario they appear in, but most of my boys overall are pretty much completely pansexual, with some small leanings here and there but overall so are they hella pan, or bi.
As I headcanon in monster culture that, unlike humans, so is there no definite sexualities in monster society, they haven’t needed any names for their sexualities.
Since there is no stigma whatsoever if you love someone of the same gender or is not interested at all etc, thanks to all monsters been so overly diverse and that there have never been any so called stigma thanks to religion etc, to change that.
They love whoever they want to, or don’t it’s all up to each individual monsters, so pretty much all monsterkind is pretty much pansexual or bisexual, with some few who are not.
For example, Undyne who is a whole ass lesbian, and Mettaton who is asexual, in my headcanon at least. But while it’s a bit strange to only be interested in one gender or not been interested at all, so is there absolutely no stigma or hate happening.
With that explained, let’s return to the boys.
Most of them are completely pan, or bi, they don’t really care or have a preference when it comes to gender overall.
Though some do have some small things they prefer when it comes to appearance and stuff, some leans a little bit more towards one specific gender a tiny bit. But overall none of them cares what you got in them pants, if they like you they like you, simple as that.
But some of them aren’t only pan/bi tho, for example, Stretch; he is also demisexual, it takes a bit for him to grow romantic feelings for someone, he needs a proper friendship connection before romance starts. He is also poly, up for having more than one partner at a time.
Though I almost forgot tho, my G snas boi Gans, he is completely aro/ace. And is the only one out of my boys to be so.
Technically though, I don’t have proper or set sexualities overall for most of the boys, as they don’t fully need it anyway thanks to my headcanon about monster sexualities overall, they will fall in love no matter what the person identifies as or got in them pants.
And while some, like Stretch above, do have some small preferences, so is this post already getting so long, so if you want to know more like proper specifics then send in another ask ye.
The only exception to the whole sexualities and this ask tho; are my pirate boys.
Since they all were originally humans before dying and becoming cursed skeletons, so is it only right that they all got properly named sexualities. Since they have not grown up in proper monster culture and are not originally monsters, unlike my other boys.
So Boney; he is a gay demi bisexual, it takes a bit for him to fall properly in love but this more out of trauma and fear of actually falling in love, but he does lean a bit more towards men overall. This is why I say he identifies as a gay bisexual, easier for him to get interested in a man, or someone who is more masculine overall, but he can still fall for someone who is a woman or nonbinary etc.
Pass on the other hand is completely pansexual, he literally has no preference like at all, if he likes you he likes you and that’s that. He is also very poly, but it is something he technically doesn’t fully need, as he adapts himself to his partner, if they aren’t okay with adding more people into their relationship so is he completely okay with that.
Then there is my Seafell pap boy Crow, who is completely and utterly gay. Men is the only way he rolls, the gayest ex pirate there ever was.
I haven’t properly thought out the rest of my other pirate boys, but I do have my female versions of Boney and Pass, aka Bon and Nessie. Though Nessie is like pretty much the exact same as Pass though so I’mma skip her.
Bon tho, she is very much a lesbian. A complete and utter lesbian.
And that’s all ya get for now yeah.