I see this as a bit of a Russell's teapot scenario: until I meet/realise I have a soulmate, I've got no particular reason to believe one exists.
This is confused by the fact I've currently got a girlfriend. Is she actually my 'soulmate'? Who knows. So, from that uncertainty I could probably infer that she isn't. Therefore, to believe in such a thing as a 'soulmate' would simply invalidate my current relationship.