First of all you have to wait a little to be boyfriend and girlfriend, first be more friends, that confection was very fast, that "like" sounded the same as when Chisaki told Kanako that he liked sex and it wasn't like that, Manaka still has the present past and the sex she had with her ex-boyfriend she still remembers because she felt good with him, and he was also the one who took her virginity, the letter he wrote to Ueno were not real feelings he only did it because of the pressure he had on his friends and a little from his sister, she still can't start a relationship with Ueno if she hasn't forgotten their past relationship, and the other thing is that if Ueno and Manaka get to have sex they won't enjoy it because Ueno is the type of man who lets himself be dominated but he doesn't dominate while Manaka likes to be dominated and the worst thing is that she is sexually frustrated that's why if they get to have sex and if she doesn't enjoy it the problem can get more complicated for me they shouldn't be boyfriend and girlfriend for the moment, and since Ueno wants to stop being perverted the problem would be bigger for them both and it would be an unstable relationship.