Answer:
One more than a duet.
What can you never get rid of when you lose it?
How do you spell hard water with only three letters?
I never was but am always to be, and everyone looks forward to me
What fastens two people yet touches only one?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.