"I was so attracted to him/her the moment we met, I just had to see where it would go-- and it led to love."

THIS.

I think there's an instantaneous attraction - both physical and mental - that can make you more drawn to a person, which will make it easier for you to become a couple (i.e. overlooking things you might otherwise consider "dealbreakers", stuff like that). But you can't love a person instantly. I 'knew' on an emotional level pretty early on with Paul that I could spend the rest of my life with him, but I still considered it on an intellectual level for two years before actually making that commitment.