Spoiler
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He drugged him and tried to rape him. He stopped because he saw the face of his former love. For years also he made yujin undress so he can watch him. Harold was a pedophile. The Campbell family is one of the worst. They are still verbally attacking the victim as a trash, as a whole, etc. He was a child. Disgusting people.
Spoiler
Because he felt guilty. He was "trying to rectify" his doings. Mind you Harold took the son of his love as a child from the orphanage, throw him in a small house without any company, didn't provide him with anything other than food, not even teaching him how to read and write and he was waiting for yujin to turn into an omega to use him. But dared to ask forgiveness.

Came back from reading the novel it makes me so sick how yujin was groomed by harold i could feel his anxiety through the screen.