Limerence refers to an involuntary cognitive and emotional state of intense romantic desire for another person.
Dorothy Tennov, PsychologistIt's a near obsession form of romantic love which is a kind of unrealistic expectation, like an infatuation, without the knowledge of the admired person. Thank god I'm out of it. This intensity can lasts for months or years and cause an emotional breakdown and probably even drastic measures of unrequited love. You can actually build a big picture of yourself and the person involved in a future that doesn't exist and live through it as though it's real.
Sounds very much like Fatal Attraction doesn't it?