"I didn't turn him down correctly"
nah you told him you didn't want to date him and he took it super personally like the thin-skinned shit he was (probably still is).
But MC affirmed that sentiment, further encouraged her, and offered full support in whatever she wanted to accomplish, so points to him for that.
Oh come on, at least make it a dating story that goes sour ...
... there's just something superficial to this manga; like it shies away from taking any steps that add something beyond the most surface-level story beats.
I don't think that's necessary to find him. If this follows the usual pattern, expect 'that' guy appear/transfer in/get introduced in an arranged marriage in a few chapters to annoy the hell out of our couple/story/readers...