Kimi ni Koisuru Hazu ga Nai: Tokimeki-hen

Kitaooji, a handsome salaryman who's also a shoujo manga otaku, has become lovers with his colleague, Arima. He is so madly in love with the cool, strong, and cute Arima that he ended up seeking Arima out too often at night. Just when he thought he really should restrain himself and started to do so, Kitaooji found out that Arima has been lying to him and avoiding him!?

(Source: Shinshokan, translated)