I just love this quote. It is so common among humans to hold the belief that "I can only be happy when I find my 'soulmate'. This concept is rampant and is usually not even questioned until the man or woman of our dreams dies, rejects us, or demonstrates some objectionable behaviors.
So... let's really take a look at it.
Say you find yourself without a mate. You have only fond memories and the truth is "it's over". Before you go looking for someone else to 'complete' you, let's really inquire to see what's going on. What is it that you are really looking for?
You just want to be happy right? Can you just be happy right now in this moment? Isn't it the belief that you need someone in order to be happy that is the lie?
You need someone to be happy. Is it true?
Who were you before you had that thought?
The Truth is... YOU = Happiness. But when we believe that we need someone to be happy, then suddenly we feel depressed, lacking, unhappy, you name it. All those emotions just happened in response to believing that thought.
Now try on this turnaround: "I don't need anyone to be happy." Isn't this more true? Give yourself several examples of how this is true. Prove it to yourself! Because you can't fool you. You ARE the one you've been waiting for!