@aznkidx she already knows that he likes her, but she's too embarrassed to be the one to take the first step and he's too stubborn about keeping his promise to himself to take the first step.
@anotherone I think this logic is due to this being an adaptation of the light novel. In the light novel, the reason why Naofumi chose Raphtalia was because she reminded him of Mein. So his assumption must have subconciously stemmed from his initial impression of Raphtalia. And it is also...