I just finished devouring Paulo Coelho's The Zahir. It is a sweeping novel that investigates the lessons to be learned in truly loving another. While I don't think he had in mind the Twin Soul relationship, some of the lessons Coelho ponders do apply.
For example, I think one of the central points in the book is crucial, which is that one must empty oneself of oneself in order to be fully open to love and to loving another. In The Gemini Bond, Trey touches on that theme when he speaks of balancing the mortal with the divine and of unifying the male and female aspects of the self. Of course, he said it much better than I am here (blatant teaser alert).
Above all, I think Coelho and I agree that being with one's Beloved doesn't equal a Hollywood happy ending. Reuniting with one's Twin Soul isn't a goal, but a process of preparing oneself for the next level of existence on the spiritual plane. Like Coelho wrote, if you change yourself, the whole world will change.
The world certainly needs it.