Thanks to songsearch and the opportunity to look up song titles by lyric fragments, I’m not reduced to asking this question TOO often, but this is one of those where I don’t know enough of the lyrics for that approach to be useful.
Song is a coed duet, mellow romantic pop of the sort that you’d hear most often on stations that also play top 40 hip hop and club / disco mix, but with crossover to “mellow rock” and “smooth jazz” stations.
Guy starts first, and sings mainly in the lower portion of his register. She comes in with an alternating section that has a different melody line and slightly more syncopated rhythm, and later they harmonize.
Here is a short (6 second) and far-from-precise MP3 fragment of me picking out the opening melody; it should be enough for you to recognize it if you’ve heard it.
(What I need, of course, is the bloody song title and if possible the performers’ names)