Depends on how we define "what hurts Sumin"
Nerver know that there are more than one definition.
Well, sungji might feel fed-up with all bullshit happened lately and retreat herself. It doesn't solve problem like what you said, but her problem will disappear since she is away from the source of the problem (aka sumin) lol
I don't think any problem can dissapear by doing that. Her solution would work iff she could make Sumin's memory of her completely erased.
I wonder why sungji insist to moving in (living together), while sumin reluctant about it. Her asking to moving in might be a test for sumin, yet what sungji got is sumin gloomy face after hearing a rumor about seju.
It's just what Sungji wanted. I don't think she was having any special intention when saying that.
I will retreat myself if I know my gf still has leftover feeling with her ex... after I told her that I am not okay with it, yet she still can't forget her ex completely.
How about you?
I would take it lightly considering my gf's ex's circumstance.