She's wondering whether she wears boy clothes because she wants to be a boy. She's wondering if this has implications on her love life. She is explicitly questioning her gender identity. This isn't something exclusive to trans people - many cis people struggle with gender identity due to not fitting gender stereotypes.
I just want to say this is why I feel so
seen by Haru and this extra chapter in particular. There’s so much nuance here and to say it has nothing to do with gender would really do Haru and the brilliant writing a great disservice.
That question of “am I wearing boy clothes because I want to be a boy?” and that relating to her struggles with understanding who she is, with wondering what gender her partner would be if she had one… it’s so reminiscent of struggles and ponderings that so many people (cis people included, as you pointed out) go through, simply because gender and one’s relationship to it can be so messy and so complicated and yet so simple, all at the same time. It’s so so real and raw and intensely touching.
And I want to point out that while Haru’s initial question to the teacher is about love, the teacher sees this for what it really is (seriously beautiful and heartfelt writing here), and simply tells her to take her time figuring herself out, finding herself… with the reassurance that those that she cares for will always willingly give her that time.
That affirmation is so important, and I’d argue that if this weren’t about gender, that teacher would have given a different response entirely.
Anyway, wow I love this manga so much.