Looking for the Oneshot Shoujo Manga about a guy with split personality
Out of the five I've found, this one fits the closest:

Blackberry


  Ever since Fune Momohara was told that she was just like a "guy
  friend" by the boy she liked, she's been bent on becoming the ideal
  girl. But when she meets the perfect guy who turns out to be more than
  a little pretentious, she realizes that it can be difficult to keep up
  appearances!