Chiiko hasn't thought about marriage + marriage = bad based on what she witnessed with her parents. At least right now she doesn't care about marriage.
So, her not wanting to is expected.
Satoshi then making it all about himself is not helpful at all.
He shoulda talked about marriage beforehand instead of totally getting into a 'I wanna get married'-kinda mood by himself and making all these plans + proposing.
Right now, they don't even know what marriage means to each other and why the other one wants/doesn't want to get married.
But yeah, I have faith it's fine, they will make up and learn from this and improve their comms.
You're right, but I'd add that you can't really blame Satoshi for having pretty standard expectations about marriage while also being understanding of Chiiko's hangups over the same.
Its a bad situation for the both of them, but one that exemplifies the persistent differences between them. Chiiko is straightforward and casual, uncomfortable with expressing positive emotions, and wants full control of her own agenda out of an insecurity that she will otherwise be let down. Marriage in her mind just ties her down, cuts off escape routes, and is pointless anyway because they already both love each other. She has nothing to prove by it.
Satoshi is passive and needy, wanting reassurance, trying to live up to standards he has for himself that he is never certain he'll reach. Marriage in his mind is a way to take on responsibility, as expected of a man, and would settle the nagging doubt that she is his as much as he is hers.
They set themselves up for failure before they started, not just by a lack of communication, and not really through incompatibility, but by their situation bringing these aspects of themselves into sharp relief. There's a sort of inevitability about it which makes this story ring so true and feel compelling to read.