I don't think Keigo did anything wrong. He's in a position where he's being pursued, but should he really be aggressively impolite in discouraging the model guy? He doesn't really have that chance since the model dude does most of his pursuing in front of Chihiro's family, clever model dude. Keigo has no choice but to be polite unless he wants to out himself, which would be okay, but he doesn't have Chihiro's permission to out him as well. Chihiro's got enormous advantages over Mr Model, but his problem is not having enough confidence in their relationship to not let the model guy bother him.
I don't think Keigo did anything wrong. He's in a position where he's being pursued, but should he really be aggressively impolite in discouraging the model guy? He doesn't really have that chance since the model dude does most of his pursuing in front of Chihiro's family, clever model dude. Keigo has no choice but to be polite unless he wants to out himself, which would be okay, but he doesn't have Chihiro's permission to out him as well. Chihiro's got enormous advantages over Mr Model, but his problem is not having enough confidence in their relationship to not let the model guy bother him.