I disagree, I believe there ARE soulmates and that you don't have to be limitied to one. I've always thought of a soulmate as someone you were really close friends with in your pre-earth spiritual life and in this life and they don't necessarily manifest as your spouse or partner although I would think that your closest friend in the preexistence would most likely be your life partner here on Earth.
People we knew before we were born most likely in our lives today as friends, family, co-workers, spouses or lovers. At least that's always been my understanding. :P