our boi needs more confidence in himself, pulling someone like her is no easy feat.
I imagine a good chunk of it is wrapped up in 1) the older brother telling him when they were younger that certain "Kyoto phrases" meant something they did not, and 2) the FL
does have ways of speaking, because of the dialect difference, that he cannot parse and thus takes in the wrong way.
So it's an actual linguistic issue of miscommunication,
but the FL also is historically incapable of conveying her feelings, when she even has them at all.
Coupling that with the fact that our ML tries his hardest but can't measure up academically to her, and is being told by....more than a couple people around him that he's not worthy of her, including her older brother,
will wear him down.
He's, like, 16 at the most. Anxiety during puberty is common outside of hyper-stressful settings like competitive high schools in the Japanese school system, and that's without having a secret engagement to someone who's seen as a school idol, who can't properly communicate her feelings for him in a way he can actually (literally) parse.