Ryu Yoonmi did not say those words just because of spite on how her pride felt attacked; there were other motives behind it as well.
One of the reasons was that she wanted to get closer to Kim Hyungsik. It would be great if she was labeled as a friend by him by the end of this.
Certainly, she was aware of how defensive the man was despite of how friendly he seemed, and being a real friend to him will be taking months for her.
But although the relationship would be hollow, she would still consider it to be an achievement if she was regarded something other than Eunwoo's fiancee by him.
It was clearly visible how he had trust issues, seeing how he wasn't that close to anyone other than Eunwoo. This showed how he put a barrier around him that was hard to penetrate through.
