Just to add, I think that Kimmer and AJ et al are making very important distinctions regarding the origination of the term soul mate as first brought about by Plato, by way of Aristophanes.
Are they talking about love?
The modern day interpretation may be more akin to the human desire to find a deep, meaningful, intimate connection, or love, with another.
I'd submit it exists within us.
I'd further submit and agree with Cadet that it's existence would be a choice...
The purpose?
Perhaps, as Kimmer describes as discussed by way of her reading, that it is potentially the desire of humans, for growth...
So is the question really... are soul mates... life mates...?