This is just your cliché yaoi manga. I was tired of ukes like Shinobu. When I started reading this, I was like 'Ah,... another one'. Once Kou cheated on him, it was expected and I wasn't happy but not too angry either. But Shinobu's change was a great + to him as a character. This doesn't get a bad rating from me because of how Shinobu developed.
Hina wa Mitsuiro no Koi ni Torawareru