That is she pretends to be the main characters friend and acts sweet and innocent but she actively betrays her by trying to steal her boyfriends and tries to turn other people against her all to one up her. She’s obsessed with having what the Mc has and wants to be better than her in order to win against her. She’ll go out of her way to make the Mc miserable out of spite

Hmm I can't remember much because I read it a while ago and didn't finish it but I think Nanairo Kakumei might fit the bill? The MC's friend was super manipulative and bullied the MC whenever she could