I can't seem to find the original quote and correct author for the
quotation that goes something like:  "If you love someone, set them
free, for if they return, they were always yours. And if they don't,
they never were. "  I've seen it attributed to everyone from Khalil
Gibran to Richard Bach to Sting to anon.  What is the "real" quote and
who actually thunk it up first?

I suspect that we have here one of those ubiquitous quotes whose true
source may never be found. As you've mentioned, attributions are wide
and varied.

I know the quote is at least four decades old; it appeared on a poster
that was popular during my college days in the 1960s, attributed to
"Author Anonymous." That guy sure wrote a lot of stuff. ;-)

There are many variants. Here's my favorite:

If you love something, set it free. If it comes back to you, it is
yours... If it doesn't, it was never meant to be.

But, if it just sits in your living room, messes up your stuff,
watches your TV, eats your food, takes your money, and doesn't appear
to realize that you've set it free... chances are, you either married
it or gave birth to it.