This site attributes it to Dolly Parton and Porter Wagoner. Guess I'd better find my Trio album and find out for sure.
-Joe Offer-

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THE PAIN OF LOVING YOU

Oh, the pain of loving you
Oh, the misery I go through
Never knowing what to do
Oh, the pain of loving you

You just can't stand to see me happy
Seems you hurt me all you can
Still I go on loving you
But I never understand

Written by        : Dolly Parton / Porter Wagoner
From the album        : Trio
Label               : Warner Bros Records 7599 25491-2 (1987)