Yes, this so much. Questioning yourself for years on end, wondering why every teen around you seems to finally have lost their mind, feeling shame that you don't feel that tingle when it comes to real people, but even more shame when you seem to react to fictional characters (there's a name for that, as well, and it also falls on the ace spectrum).
Growing up like that was... not easy. And not knowing that I'm both on the ace spectrum and biromantic, and consequently thinking that I have to perform sexuality with men was scarring. I can't count the times where I engaged in sex even though I was not interested in it, just disgusted in the end that I allowed them to use me (because that's what it was: coercion on their part, always). >_>
So, if a narrative doesn't even touch on thoughts like that, even though it's set in a world akin to ours? That's all the proof you need that it's not about a demisexual person.
Welp. Didn't mean to disclose something so personal, but maybe it helps others distinguishing between these chastity tropes and true demisexuality.
What do you think is the reason that it's mostly female characters that are demi? Are you thinking about the hypersexualization of men in media or is it something else, too?
As for the demisexual men: I have one, hidden deeeeeply in my WIPs lol; I struggle with writing people that are 100% like me (so if someone's demi in my work, they're most definitely NOT a woman xD), so he is the closest thing to myself that I ever concocted (including depression and paranoia I had in my darkest times /hides).
Maybe I should pick up his story again sometime. 
