Once you have found true love at the core of your being, you are complete. You don't need anything outside of yourself to complete you. You may delight in sharing the love that you are with another being. But you definitely do not need that to complete you.
Suppose, rather than going inwards to find true love, you searched the world until you found that one person that you think "completes you" and you fall madly "in love". What happens when she dies? You are "incomplete" again?
Bingo. Good relationships are made up of two wholes, not two parts of a whole.