As far as I know, these twins have liked Seonwo since school days, but Jaehyun did something fatal in the past that made him do whatever Junwo told him to do. So the question is why Seonwo doesn't remember who Jaehyun and Junwo are... the only ones who remember are the twins. That's all, so it's not surprising that now around Seonwo, Jaehyun becomes even more obsessed with being afraid of being snatched by his older brother, Junwo.
As far as I know, these twins have liked Seonwo since school days, but Jaehyun did something fatal in the past that made him do whatever Junwo told him to do. So the question is why Seonwo doesn't remember who Jaehyun and Junwo are... the only ones who remember are the twins. That's all, so it's not surprising that now around Seonwo, Jaehyun becomes even more obsessed with being afraid of being snatched by his older brother, Junwo.