i think they're talking about how the goh attached to the guy - that since it's a lover's goh/curse or something, he must be the lover that the girl so badly loved to the point she wanted to kill them.
it's still definitely confusing but i have this theory where he's not the lover.. remember how the girl mentioned her boyfriend when they met? i feel like that was the lover she was actually talking about - also, the guy (the one that made the lover's goh) talked about how the lover's goh is not limited to lovers, it could be someone you cherish.. and the girl mentioned that mc was the only boy nice to her throughout her life so that's saying something? i feel like what actually happened was the girl couldn't go through with killing the man she loved, her boyfriend so she opted to mc, someone that was nice to her bcs in a way she cherishes him? i don’t know honestly, i just missed talking about theories with strangers in this site haha
i think the guy (seojin) is not the target of the goh, the girl was "gifting" seojin the goh after she was done with it because she thought he also has an unresolved love grudge. they mention that after it's done it attaches to the next person with a strong grudge to touch it. seems like something happened in the past that seojin doesn't remember. but i kinda suspect seojin's grudge victim is not his brother but actually yunhee...
oh!! i thought of the gifting part too but i didn’t think of that reason!! THAT ACTUALLY MAKES SO MUCH MORE SENSE THANK YOU and honestly now that you point it out, the grudge victim may not be his brother and is actually that guy becauuuuse well how will the drama start if not haha, kidding, all jokes aside, THANK YOUR FOR THAT, NOW I UNDERSTAND A FEW MORE THINGS

Can anyone tell what happened in ch 5 ?! It's confusing