pretty sure the MC did a mistake in choosing his words while confessing to the superior....
instead of asking her to come to his place, he should've said he liked her, i bet she kind of liked him too since she did agree to the date, and was disappointed with his way of saying i like you. most probably she had similar experience of man picking her up due to her "body" instead or personality, and the MC made that mistake i guess... misunderstanding ftw!
we'll see how things goes later... this was my take on the situation, but it could be wrong and Gotou do have a BF, but i doubt it....