To be honest, why does it happen so fast? Because it's not love in the first place. It's an obsessive-trait. With Most people that say that they fall in love with someone fast if you really look at it, it wasn't love at all. Love is a word that involves truly caring for a person deeply and goes way beyond the things you feel when you're obsessed/infatuated with someone that happens to be your focus of attention at the time. Think about it, you say love but ... you think of this person and are engrossed in fantasy, feelings and ruminations about being with them all the time. you panic, freak out and lose control because you think they are gone, abandoning you or are ignoring you. This is not love at all. I say this all from my own experience. To this day, I am not sure that any of the women I obsessed about were women I was in love with in the beginning. True, I may have loved one of them but it wasn't in the beginning, it was what grew from a longer term relationship.

Don't mistake your obsessive need to have someone as love.