Yes, thank you, Monique, I understand what you're saying about the meaning of "maîtresses". It's just a bit strange that, having said "adieu" to the "filles" in the first line, they seem to be about to go on and see the "maîtresses" at the end of the verse, which seems to suggest that these are a different group of women. But maybe they are just planning to say one more final farewell to their respective lovers?

Any idea how old the song is?

Marje