That whole "soul mate" thing...I'm not sure I buy it. What she's probably trying to say is that she feels a really deep connection with this guy but the good news is that it's purely platonic. Since I tend to be on the jealous side, I would find this uncomfortable just because I would want my partner to have that kind of connection with
me instead of a friend of the opposite sex, but the thing is, those kinds of relationships don't necessarily translate to the best love matches. I've met guys before that I've gotten along with like no other, and we had so much in common it was scary, but they made better friends than boyfriends. Who wants to date someone who's a version of yourself?
If I were you, I would only get riled up if she gives her friendship with this guy higher priority than your relationship, all that "soul mate" crap be damned.