My Girlfriend has multiple personalities is a Manga/Manhwa/Manhua in english language, ROMANCE series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Narita doesn't believe in love at first sight, but when he meets a cute high school girl named Tsubasa, he falls for her immediately and even confesses to her. They both decide to start out as friends, but then she comes out and tells him the she has multiple personalities...!?