JOEL - As far as I know there is no truth to this. There is nothing doctrinal about the idea of having a predetermined "soul mate". It is a simple term that is often used to describe two people who seem to get along with each other, who have similar likes and dislikes and often times know what each other is thinking or feeling. The idea of a pre-determined soul mate was made somewhat popular by the LDS musical "Saturday's Warrior", but it is mostly romantic fiction, not really supported by scripture.

In regards to marriage partners President Spencer W. Kimball said:
“Soul mates” are fiction and an illusion; and while every young man and young woman will seek with all diligence and prayerfulness to find a mate with whom life can be most compatible and beautiful, yet it is certain that almost any good man and any good woman can have happiness and a successful marriage if both are willing to pay the price. (Marriage and Divorce (1976), 16.)

Boyd K. Packer said:
“While I am sure some young couples have some special guidance in getting together, I do not believe in predestined love. If you desire the inspiration of the Lord in this crucial decision, you must live the standards of the Church, and you must pray constantly for the wisdom to recognize those qualities upon which a successful union may be based. You must do the choosing, rather than to seek for some one-and-only so-called soul mate, chosen for you by someone else and waiting for you.”(Eternal Love, Deseret Book, 1973, p. 11.)

The First Presidency stated:
"We have no revealed word to the effect that when we were in the pre-existent state we chose our parents and husbands and wives." (First Presidency, June 14th, 1971)

Some people may get the feeling that they knew each other in the pre-earth life; something that is possible. But believing that they were pre-destined to be together in this life is not supported by scripture or latter-day revelation. I don't believe that soul mates really exist until you meet someone and make them your soul mate as described by brothers Packer and Kimball.