Making Guacamole All Night Long

So I was whipping up a batch of guacamole for dinner, listening to the Texas Tornados (I am eternally grateful to Egg for the CD). On comes their classic, "Who were you thinking of when we were loving last night." I began to wonder about the ethics of it. The lyrics go,

"You got more out of it than I put into it last night.
Who were you thinking of when we were loving last night,
was it a good looking stranger or a close friend of mine?
Who were you thinking of when we were loving last night?"

Is this betrayal? The partner didn't actually do anything with anyone else. Having "lust in your heart" ala Jimmy Carter as is certainly not as bad as having lust in your office ala Bill Clinton. No matter how committed you are to your partner, there are always people in the world who you find attractive. But does it make a moral difference if the image pops up mid-coupling?