A friend once told me a funny observation on relationships: friends who were single wanted to be in a relationship while friends who were in a relationship wanted to be free.
Seems like everybody desires to be something what is not here and now, but as soon as the target is achieved, the desire is shifting to another target.
Let’s look at the desire to be in a relationship:
This is not really about being in a relationship, but about the fullfillments of needs: physical & spiritual comfort & exchange of energies.
Looking at these separate needs, it looks like each of them are already being partly fullfilled in different settings and circumstances.
Now comes the tricky part: the desire is moving to another new target, wishing all these needs could be fullfilled by the true soul-mate.
So it seems the desire will never be fullfilled, there is always the next horizon beckoning.
The only way of fullfilling my desire is to enjoy the fullfillment of this moment, while acknowledging the craving for the next fix.

See also:
The Desire Map • Danielle LaPorte: white hot truth + sermons on life