It has been interesting to view the replies…I have a different view of the concept of a “stable” . Some may disagree but I think the term “stable” has evolved over time and seems to know be used in a more particular manner than it used to be. Stay with me for some old timey, “back in the day” stuff.
In the 80s and early 90s…really until the widespread use of the cellphone (more than even the internet) moving from seeing mistresses at session houses to independents was a laborious process. Even in a city the size of NY they were relatively rare and one had to scour the ads in places as varied as New York Magazine, the Village Voice, the “Hells Belles” section of Screw Magazine and Dominant Mystique, etc. to find independent Mistresses. You then might have sent a snail mail letter with a SASE, or maybe called an answering machine and listened for specific phone hours and hoped to get through at that time. At the end of all this you (hopefully) had an appointment and, if all went well, started to see that person on a regular basis.
And it is there, in my memory, that you became part of a “stable”. It was a bit of a euphemism for “regular”. The more modern usage seems to be focused towards those who have a deeper personal connection.
This is of course a personal memory, albeit one informed by almost 40 years of sessioning at this point, and other recollections may vary. Language is malleable and meanings and context change and in my “scene” experience this is only one (of many I can think of) example of it.