I've said this before and I'll say it again; I think the whole idea of soulmates is a dangerous one . The saducees asked Christ a similar question (Matt. 22:23-33) which we should not ignore. Soulmates (the very term of which) implies that there is something beyond this earth (something spiritual) to such a union. (that's not biblical...unless you are willing to take the view that ever believer will be your soulmate...which defeats the purpose of the concept of soulmates in the first place).
I think most that do take this soulmate concept, take it in hindsight of their situation (i.e. I met lydia (fictitious character) and i can't imagine being with anyone else, hence she is my soulmate). There is nothing wrong with that, but like the saducees I'd ask, who was Elizabeth Elliots soulmate? (Liz elliot married 4 times...previous husbands died).
I think another danger (which I don't accuse present company of doing) is allowing the soulmate theory drive the relationship. You see, the idea of soulmate means, this is the one person for you, so if they are out of line, hmm...maybe this was not the person for me, have I made a mistake? In today's society divorce is not frowned upon for many reasons, one of which is: "she wasn't the one for me", "I met my soulmate". The nature of marriage is such that it is hard work, discipline, commitment, and as a wise recently married friend of mine once said "it beats out any ounce of selfishness you have". But I should digress (and turn around)

because I'm preaching to the choir.
Now, I am not so bold to say I have it figured out how God does this. But I lean more towards to concept or theory that states there are many people that are compatible for you, some you will meet and some you won't, but the one you choose is your life partner (until death or divorce (in acceptable cases)).
But officially, my stance is this:
Prov 30:19
"There are three things that are too amazing for me,
four that I do not understand:
the way of an eagle in the sky,
the way of a snake on a rock,
the way of a ship on the high seas,
and the way of a man with a maiden."
Whatever theory you side with, I think we can all agree that God is in control. Amen?