Regardless, the dramatic shift for Soeun was the fact she used to let her oppa know what was happening, or they'd plan for it like that beginning foursome.
Now though, Soeun is acting more independently, there's been a lot of instances where she fucks someone without telling her oppa but he always finds out once way or another.
But this shift, and the scene with the gang member, made him get the feeling he's holding her back, hence the push to break up with Soeun.
But yea I'm just in it for the art mostly!