Psychologist here! Simply put, people subconciously learn behavior patterns when growing up and interacting with others, regardless of said patterns being nice or painful/traumatic. For example, if you grew up with abusive parents who miscomunicated and blamed you for things, you may replicate that same behavior with a romantic partner, even knowing how much it hurt you in the past. Because it's the only way you've experienced close relationships and the habit has turned it into some sort of "comfort zone" to interact. People end up "fearing" healthy relationships because of how uncomfortable it feels to not know how to be in one. Like when you see people resisting and avoiding direct cunication to solve a personal problem.
I'm always wondering(not because it always happen in some manhwa's but also because this thing sometimes happens irl) why do some people who have mental illness or a trauma,they'll do the same to other people for them to also experience what they went through,do they feel fine after ruining another person's life? I'm always trying to find ways to understand on why some of them do this but-