Mr. Fukube Doesn't Need a Girlfriend! ~He Said Love Was a Hassle, but His Love Is Just Too Heavy~

Yui Itomura is in love with her teacher, Seiichirou Hattori, who already has a girlfriend... until she finds out that his having a girlfriend has been a lie, at which point she decides to confess her feelings to him. He initially rejects her on the basis that he finds romantic endeavors troublesome, but things escalate when Yui seduces him, awakening his instincts as a man. After having sex together for the first time, he begins to desire her more and more. Their relationship is secret and purely physical at first, but their hearts are slowly closing the gap. However, a certain incident leads Yui to ghost her teacher. By the time he finds her again, he's already consumed by obsession. He forcibly takes her to his house where he repeatedly violates her with pleasure while whispering words of love. It's his way of ensuring she belongs to him... (Source: DLsite)