I Should Not Love You (manga)

Since he was little, Taisei Fujima has been known as the pretty boy in his town, and throughout his pampered and self-indulgent life thus far, there has only been one thing standing in his way: Keita Okachimachi, his former middle school classmate. Therefore, when Taisei is once again reunited with Okachimachi, after three long years apart, Taisei can't help but get riled up. And thus begins Taisei's grand plan for revenge...! Except, something's wrong.

Even though he loathes Okachimachi with every fiber of his being, why is Taisei's heart beating so fast that he can hardly think straight. "Don't tell me I've fallen in love with him-?!"