The only one I could find on iTunes was "My Girlfriend's Boyfriend
Isn't Me," by Autograph, on their album "Sign in Please," released in
1984.
It's not poly-positive. Is this the song you mean?
Yes . . . I thought it WAS poly positive. A little wry sometimes
about the poly experience, but I took it positively. The line, "So
you're Mormon, right?" really cracked me up.