That is an interesting question, johnh. I mean, the whole song seems to relate to a current, happy relationship, except that line. It has always stood out to me as well. I have a couple of theories, either:
the song is telling a story from different view points/perspectives, as in SSS
or if you listen to the lyrics, all of the song is referencing a love that was only a fleet moment in time, except the verse that Bonnie sings in the sentimental version.
I could go on and on, interested to hear what you and the op think.