"so, let love and your heart be your guide.. and let
your head do the work to smooth the path.."
Read through all posts including Yun's very technical reply hehe
but I think that bear's the best answer.
One thing for sure, anything can happen in the future. Hence, the
right partner is a game of trial and error. If you are lucky, your
first will be your last. When you reached your final breath, ask
yourself, "If I were to start life all over again and fall in love
again, would I choose the same guy?" If your answer is yes, then he
is the one.
In this world with billions of people, only one perfect one for us?
We may never know unless we met every single person and know them
inside out, and finally decides on the chosen one. You may have
chosen your one now, but hey, for all you know, I could be a better
partner than your current. Heck! That guy over there could be a
better one too!
Everyday that passes by with your partner, your feelings towards
him/her determines the chances of him/her being the One for you.
Once you no longer feels the same way, the chances of him/her being
the One for you? Possibly zilch.
Things get complicated because it is a two way thing. You may love
him all your life but the guy may not. So I'm guessing the quote
from bear is the best answer to your question. 