Even if he doesn't hold it against her, as Nietsche said "I'm not upset that you lied to me, I'm upset that from now on I can't trust you." Even if they do get back up he would have to be extremely naive to grant her the same level of trust he did previously, even if he was that naive he won't forget because her body is covered in tattoos that remind him of it. The power dynamic is also entirely different, Yuumi will be completely submissive to Hiroki, whether that is wanting to play a "baka couple" or simply her being his sex slave, she has no choice in the matter. Her happiness, her choice, her desires, dreams, future, all irrelevant to Hiroki. Unlike that black guy, Hiroki will have complete and total power over her because he controls a human need far more important than sexual satisfaction. One can go for decades without sex, but humans are so dependent upon other humans for companionship, having no friends, no family, no lovers, nobody who you can trust and rely on can quite literally drive a person insane. In order to fulfil this desire, Yuumi will now sink to any level Hiroki demands simply because he is willing to speak with her.