Nakaizumi Yuuji

He has liked Miori for quite a while, but knowing that she has a boyfriend, he has given up on her. However, upon hearing that they broke up, he made his move and they started dating. From then on he lives a happy life with his girlfriend.

However, on the night of their first year anniversary, he went to Miori's room to surprise her but instead he witnessed her having sex with another man.

[Translated from Official Site