The mom is doing what she did to the older brother to Jaemin. He hides behind a smile and little by little takes it all until he cracks. He would have probably gone down the same route if he didn't have his friends.
Let me guess she used to be fat or ugly. I hope the girl is genuine in trying to be her friend and not two faced. The seasoned veteran webtoon reader in me says she has an ulterior motive.
The chapters are getting shorter and almost feel cut off. This webtoon started off so good but just got lost somewhere. MC was likable in the beginning and they showcased her gender struggle. Somewhere along the way it's like the author dropped that and now it's about a girl who likes a guy...