“Since at the beginning of an attraction that will become limerent, you feel both free and happy
(you walk on air), it is hard to resist once it starts.”.
“….And although it resembles a disease in some ways, I see it as a normal adaptation, an instinctual reaction, if you will, that through the course of evolutionary history proved valuable to species endurance.”.
(Dorothy Tennov, Q and A on Limerence)

Limerence:

“an involuntary cognitive and emotional state in which a person feels an intense romantic desire for another person.”.
(from Wikipedia)