How do you know they're "the one"?

I believe that you can make it work. I don't necessarily believe in "the one" concept but I do think you can find someone who you love more than any guy you've ever met. There is never one specific way to determine if he is "the one" but if this is a person that you can go from being completely comfortable with to still having that passionate love in the same day then you have found someone that you can share your life with.