I agree with the concensus of responses, that it is not in the Bible. 1 man for every woman is in the Bible, and God hates divorce which one could theorize that there is a best "choice" for all of us, however due to how messed up the world is I think with all the divorce and bad things that happen in life, those best "choices" have to be altered to next best option. Due to free will actions by humans in theory your spouse could die well before you ever met him/her, and therefore you might have the choice of being with "next best option".
In reality I feel the term Soulmates is a self-acknolwedged or self-fulfilling prophecy in that people simply reafffirm their commitment to someone by calling them their soul mate, when in fact those same people making that claim could end up divorced months, or years after making those statements.
I have been engaged twice, never married, and never met someone that I have said they are my soulmate. One of them, even though I am with someone now, I still wonder sometimes as I strongly felt that that person was the one for me, still I am not with them any longer therefore could have been and I let them go, or not at all and I either have a hang up or I was just flat out wrong, or there is no such thing as soul mates.
You really have to wonder when it says that in the Bible about 1 woman for every man etc. if that perfect spouse and the concept of a soul mate is really possible with free will, or perhaps choosing them is a free will choice, yet declaring a soul mate seems to be predestined or calvanist thinking.
Difficult.