Exactly! It's like they are just "blinded by love" but people like Kimin end up becoming abusive and controlling partners. Whether he realizes it or not, kimin will end up hurting kyueon one day, and yet he will still be loved for it. He will (and already has) made his partner begin to become used to his violence and this will be damaging to the relationships he tries to build with others and even his own mental health.
i'd just move to an another city or smth if i was in the place of Kyuyeon but considering what kind of a person Kimin is he'd definitely find him. i definitely don't read this for the romance(actually obsession) i just hope to see kyuyeon realize somethings wrong and he must end this toxic situation. either kyuyoen puts a stop or kimin changes himself for the better. because this is definitely not a healthy relationship

Sometimes I feel like they’re a little toxic. But I think the author wants it to be a overprotective kind of boyfriend ?? They’re still in high school ?? So hopefully they mature and grow comfortable with one another. And build some trust.
And what did his cousin mean by it’ll be hard.