Looking for a manga

Hello!! TTvTT

I'm looking for a manga (shojo?) its a short read,

It's about a girl who has a sex friend (not sure if they are childhood friends). She seems to be working at a fast food restaurant and the guy she has a crush on asks her out. so now she wants to cut it off with her sex friend but he gets angry and they make a bet about loosing weigh.(I cant remember the details just the fact that she gotta loose 3 kilos) then when she dose he gets her high school gym cloths then they have sex. I cant remember the rest but I wanna reread it TTvTT

Thank you in advance <3<3<3