I don't believe in soulmates. And I don't think there really is a soul, at least not in the same way (I think) that more traditionally religious types view what is at the core of humanity.
I'm an agnostic non-theist. I tend to think of the essence at the center of who I am as something like a spark or a flame, and it is the thing in me that gives me a will to live. Something like that. It's not really important to me to figure it out (as I've stated in the Religious Survey thread
But think about it: If there is supposed to someone out there who completes us, then we're incomplete until we find them. I don't believe anyone is incomplete; we just feel that way when lonely or missing something satisfying in our lives. But we are whole already. The focus on lacking something enables us to construct this wistful fantasy that someone out there will fill in those "holes" we feel in ourselves. But feelings aren't facts. We want someone to fix us somehow by making us feel
complete, but it's an illusion (how many people have divorced someone they thought was a soulmate?). There is nothing wrong with being alone if we love ourselves. We all come into the world alone and we all die alone. No one else takes those journeys with us.
Furthermore, if there is supposed to someone out there who is meant to complete us, then that, correspondingly, also means we're here to complete someone else. I just don't see that as my purpose in life.
My overview on what a human's purpose in life is not that we're here to fill in someone else's lacks, but to be on a journey on this earth and learn lessons. I see the people in my life as there to teach me lessons and learn from me. Love, as I see it, is the connecting factor in humanity -- it's the energy that fuels that spark or flame inside us, but no one is obligated or meant to love me. When we feel love for someone, or when they feel love for us, it's really more like uncovering the essence of what's already there.
That's how I see it. Investing in the notion of there being only one soulmate for each of us negates so much possibility for uncovering and feeling the love that we can have in life, and for so many valuable life lessons.