Stalker vs psycho ex boyfriend manhwa

Romance/psychological thriller manhwa about the female lead’s stalker and psycho ex boyfriend...she was blonde and the ex had red hair and was kinda delinquent-y. He dumped her bc she was fat but she got a super good body and so he was desperate to have her back...there was a scene where he hung her over a desk or something. Also there was a scene where she’s stuck with the stalker in an elevator. Please help!