You're dating Karasu without giving him your otoya. When you told Karasu that Otoya wanted you to be his girlfriend, Karasu had the idea to tell you to accept it. And let you play with it. 6 months passed since you accepted Otoya as your boyfriend, until finally Otoya found out when he saw you walking with Karasu while he was walking with another woman. He was really surprised... because he didn't think that Karasu and you had a relationship all this time.