The words that norae's friend said, " it hard to break the inner wall" is that all a lie? Why norae feel jealous now ? Its like norae wasnt that hard to fall for someone and seola did not really done some effort that can make norae falling in love with her. Can somebody explain this

I don't think norae easily fell for seola. In the beginning we can see that seola's overwhelming reputation and appearance did draw some of norae's attention, but I think what ultimately got her was seeing a side of seola that others have not seen; especially at times of vulnerability.

Seola is supposedly this campus idol with a perfect life. The whole package deal, beauty and brains yada yada. However norae sees first hand that it is not always sunshine and rainbows despite seola's reputation. She sees seola get almost choked to death and she over heard the negative gossip that seola had to deal with for years from jealous girls, but seola acts as the bigger person and withstands it all. And that scene in the stall was plain heartbreaking :(

I don't think seola broke norae's inner wall, but i do think seola unknowingly let norae into hers. Maybe that's all she needed to get the "flutters." Lolol

Also, it's been 27 chapters. I'd say that is plenty time to form connections.
....and sorry for the wall of spoilers