I got a feeling he only started to treat Haejin as a human because he accidently imprinted on him and that mean he was only able to control his pheromones in the presence of Haejin. Haejin is just deeply depressed for majority of the story, and it felt like he decided to stay with Ryle only because in this world, when you imprint on someone you suffer every pain the other person does. So he was kinda coerced into this relationship, lol.