It sounds like you are referring to the French classic Maitresse pour couple (1980).
The exact title Maitresse pour couple appears in vintage adult film databases (e.g., IAFD, EGAFD) as a French hardcore feature from 1980, starring performers such as , Catherine Ringer , or Alban Ceray — common names in French erotic cinema of that period. Maitresse Pour Couple -1980- - French Classic -
Would you like help finding where to locate the film (legal sources), or a breakdown of the cast and plot? It sounds like you are referring to the
This is likely an adult or erotic film from the late 1970s / early 1980s French cinema scene, often associated with director or producers like Alain Payet (though multiple directors worked under pseudonyms). starring performers such as