@tsuyukihime: I think that it's because the setting it's so different to us that some sexuality issues we know are almost non-existent there.
The biggest crux on this world is that gender is not fixed, but "chosen": if you feel like a girl, if you feel attacted to guys, if you like "girly" things even a bit more than boyish things; you'll become a girl. And apparently, if you don't have a gender beyond a point in age you'll die, but not having gender a that point is a very rare occurence. They can "choose", unlike us that our biological gender is set before we're born.
I think that by understanding that point, its implications and the consequences of it first, some of the things that for us look weird becomes more undestandable. For instance, the fact gender roles are more set in stone than in our world, or that homosexuality is not that known. Why would you want to be something that you've not chosen to be, even subconsciously?
Several of the gender issues in our world (not all, but several) can be traced to the fact their biological gender doesn't match the gender they feel they are or the one they want (again, it's not a layman term, but some of the terms under the LGTBQ+ umbrella most likely doesn't apply here, like probably transgenderism); that's not an issue here.
The thing with Hinase is not only gender issues, but also related to maturity, I think. He's faced with the fact that their friends are changing not only because of gender, but by adolescence; and because of that, things cannot go on the same way they were before. It can also happen in our world because when you're a kid, it doesn't matter that much if your dear friend is a boy or a girl; but come teen years and ¡pop! nothing's the same. It's a hard truth they has to face like it or not. And he's undestandably scared. It doesn't help that both his childhood friends, who are on different genders love Hinase and wants them to choose, putting even more stress on him. He's faced with gender identity, coming of age, love issues and friendship choices all at once, with an additional biological and social pressure. Really, it SUCKS to be Hinase right now.