You people also have to remember that this dude up and proposed almost immediately after having sex once and telling her "Also never ask me again because girls aren't supposed to want it."
Which was something he refused to do because he was scared of having a relationship that was more than just him eating hair.
Marriage is a big deal and the dude was indecisive and dismissive towards her for a long ass time, if I was in her situation I'd have tested him one more time too.
And you guys seem to have speed read through the fetish ban arc. The point of the arc I feel was to prove that Kotoka can go without fetishes. She loves him with or without licking his back. But the entire time he complained, whined, begged and tried to sneak in hair touching.