I am not really convinced about their relationship. Perfect match? Are they? They are kind of similar, but that's it. They are not a couple at all. Just two psychos playing house.
Yeonhwa is a sociopath, she doesn't care at all. Sometimes it seems that she has a little regret, than she bounces back in like 2 seconds. She jumped ships from Ayeon, and then from Yeonyoung without blinking an eye... As I said many times, she doesnt give a fck about anything. I am pretty sure she would be okay with anyone. Just wait until her sister or someone else appears. Hehe.
And Dahye… She has mental issues too. Probably stockholm syndrome or something, thanks to the abuse during highschool. So I am not really sure about her feelings for Yeonhwa...
Well, whatever, who cares. Every wrong decision they make brings closer my SubinxYeonyoung ship. I mean I hope so.