I definitely don't believe that there is only ONE person in the world that you could spend your whole life with. There could be two, maybe even more. You could make yourself crazy wondering "what if" haha.. what if there are TWO MORE people that you could love just as much as you love the two people you already love. haha.. yeah ...
The thing is that you can only be with one.
How you determine this I don't really know. I'm sure there are several people on the planet that I could be very happy with. However - all I know is that the person I married is the love of my life. Could it have been someone else???? It's impossible to even imagine it.
Anyways this is why it's dangerous to be too close to members of hte opposite sex once you're married, (there was a very recent article about this in I think the Awake..?) you could be "just friends" but what if you start to think "oh i could have been happy with this person" and problems arise.
I think everyone deserves to be the love of someone's life, hehe. And once you make your choice you can't think about those other possibilities .. ever, really. It's not fair to anyone involved.