hello, im a bit lost hehe... so the reason why Hime is dressing as a boy is because she do...

Probably not even she knows the real reason.
At first it was to help Akira, to be able to understand her feelings more and that Akira had a "comrade in battle", so that she wouldn´t feel alone in the school.
Then when Akira started moving forward without Hime (Making new friends, falling in love with a boy, and other things independent of Hime), Hime decided that she should also try to move forward, so she stopped wearing the male uniform.
But the boy Akira fell in love with began to see Hime "like a girl" (Treating her kindly just for having boobs, typical of teenage virgins ╮(￣▽￣)╭), and that made Akira aware that the boy had only been treating her as "a man" so far in their relationship, and that made her feel jealous of Hime, and said something painful to her.
For Hime, the idea of hurting Akira is unthinkable and unforgivable, but what hurt Akira is the social treatment of Hime's biological gender (That they treat you kindly just for having boobs, honestly I don't see it as something to be envied but each one with their opinion ┑(￣Д ￣)┍), Hamuro tells Hime the situation of his sister that she suffers from those "privileges" for being naturally cute and feminine to the point of stopping to go to school, and Hime concluded that it was her own fault for being so feminine that she was treated like a girl so she returned to the male uniform and this time being more "natural male"(╯°Д °)╯╧╧.
But the boy apparently his type of girl is "boyish or tomboy", and that made him find Hime incredibly cute, and he began to flirt with her immediately, even asking for his number from Akira, which made Hime more desperateΣ( ￣□￣||).
Hime no longer knows what she wants and Hamuro asks if she hates "being treated like a girl" or "being a girl" or "that she being a girl hurts Akira," and that she should base her opinion on what she really wants regardless of Akira, so he decides to ask her out to treat her like a girl and that she does her answer regardless of Akira.
Conclusion, Hime is just as confused as everyone(〜￣△￣)〜.

maybe she wants to be a non-binary,but she doesn't know it yet

That’s a real possibility

At first Hime didnt want people to treat her friend any different just because she is wearing female because she believes clothes doesnt define you. . . But somewhere around the line her friend used her as (shield) thinking that Hime will always be there to support her until she was accepted and got mad when all it took was dressing back to be seen as a girl and he has to struggle but he has forgotten that she has also a life. Hime then took it upon herself(because when she is alone she takes extreme measure for her friend) thinking that it's her responsibility to babysit her friend until she is ready to face the world. The new guy doesnt want that he wants her to feel that it's ok to be who you are even if it means facing your friend.

On top of being ace and aro I'm also non-binary. And, especially with the chapter you're talking about, I feel even more strongly that this is what Hime identifies as.

I think Hime doesn't like to be perceived as a girl, in gender expression, because of how different people treats girls from boys and she doesn't enjoy the romantic/sexual attention she receives as a woman.
She crossdressed to help Akira, it was an impulsive decision, a very silly one that caused more harm than good but it still led her to figure out she was not uncomfortable being seen as someone almost neutral, on the contrary, not being all that feminine was more comfortable for her.
Anyways, she might just be a cis girl who doesn't enjoy performing femininity and fitting into gender roles or might be non-binary, but there's nothing to indicate that she is actually a he aka a trans-man

That was Momo-chan's issue. Plus Hime grew her hair long not because she thought she wanted to perform femininity but because Akira said she liked it. Finally it was not a silly decision to help Akira by crossdressing herself considering that it caused people to rethink their expectations of gender performance. Even when she reverted to a more 'girlish' appearance. Their reactions might be the same when she discarded the masculine attire but that was only because they were natural reactions that they'd grown up with but now they have secondary information they can use to check their natural reactions.