Does anyone know of books with a metaphysical / soulmate theme?

I just finished The Soul's First Kiss by Gregory Isaacson (http://www.gregorywisaacson.com), and I loved it. It really got me interested in metaphysics and soulmates in general. I'd love further reading on the subject, and need recommendations! The Soul's First Kiss in a novel, but I'm open to other options (nonfiction, etc) as well. Even movies!