Is this the one?

Copied from http://norma100.com/11/11lyrics_clips_whowereyouthinkin11.htm
(That page also has a sound clip of Jim Glaser singing it.)

WHO WERE YOU THINKIN' OF
Jim Glaser, Paul Gauvin, Cathie Pelletier, © 1979, Inmy Music. (BMI)

Who were you thinkin' of
When we were makin' love, last night?
You had a smile on your face
I ain't seen in some time.

I know it wasn't me
Sharing your fantasy all night.
Who were you thinkin' of
When we were lovin' last night?

Who were you thinkin' of
When I was makin' love to you?
Some good-looking stranger,
Or was it a close friend of mine?

You got more out of it
Than I put into it; that's true.
I'd like a peek at the
Phantom you keep in your mind.

You're like a moth
That longs to touch a star.
You close your eyes
And you escape from where you are
To where you'd like to be;
Aw, but you used to fly with me.

Who were you thinkin' of
When we were makin' love last night?
Who were you yearning for
While I was burning for you?

You didn't want to quit
When we were into it, did you?
Who were you thinkin' of
When we were lovin' last night?

[Recorded by Jim Glaser, Freddy Fender, the Sir Douglas Quintet, and the Texas Tornadoes.]