Once a woman has placed a man in the friend category, it's basically impossible for her to ever see him in a romantic way. It's unfortunate, but there's probably some evolutionary reason for that.
It's different though, with men who put women in the friend category. Basically, for guys there is no friend category. There was a study done at one point, cannot remember what or when it was, but the male participants seemed to always have their friend girls on the girlfriend table.
Edit: Oh, I thought this was chapter 17 as it just released on their website. Put no spoilers in the comment though so it's all good.