don't worry, I totally understand what you mean :) Nino forgives Ohchan "quickly" because he can't kill him because he realizes how much he loves him and needs him. Plus, Ohchan was 8 years old when he killed Nino's mother, he was just a hurt child manipulated by his evil father, that's why Nino can't be hateful, after all, it's hard to hate a manipulated lost child who thought nino's mother had killed his :) the way Nino gives up on his revenge so quickly was to show the deepness of his feelings and how ohno had managed to make him more human :)
But don't worry, I understand perfectly your POV and a sad end would have been good too :) I also love DoS Ohchan xD
thank you for reading and for telling your thoughts :) I'll do my best for a new story :)