Kitahara just being realistic straight, he didn't really consider Minami as love interest before , even tough he know Minami is gay, he just too focused on women and he didn't know if his friend is considering him as love interest.
Minami just cowardly hold in his feeling because he didn't want to lose Kitahara as a friend beside him. And Kitahara kept thinking it is such a normal way to have Minami always by his side
Mukuwarenai Koi no Uranaikata