I don't really believe in "soul mates". There's matches of varying degrees, but a relationship
always requires some effort from both partners to work; there's no magical, pre-ordained total-harmony-guaranteed "soul mate" if you ask me.
That said,
someone who understands me and acepts me for who I am
that's pretty much a given if you seek a stable, lasting relationship. No functioning communication + need to put on a show even for your partner = relationship dead in the water.