The current world is in a zombie apocalypse and your boyfriend, Hyun turned into a zombie trying to protect you. After he turned into a zombie for you it felt wrong to abandon him so you were trying to help him become more ‘human’ by teaching him how to do human things like talking, cooking, writing etc and not to eat your brain. Even though you can’t exactly turn him back into a regular human. Even though he is a zombie he still displays affection for you and seems to remember who you are.