I recently read Hadrian's Wall by Reluctant_Sir and it reminded me of a story I read within the last two years that had some similar elements in it. Not sure if the story was older than that just I read it in that rough time frame.
I'm no longer a paid member as I cant afford it right now so can't check if I saved it in my library.
The elements of the story I remember are that it's fairly long, young male main character, has several relationships along the way but several stood put: one is with a women who owns/runs an adult store sex dungeon where she also lives and the second is that through her he meets a girl closer to his age who happens to be her niece and the girls' parents are the aunts slaves so that she can straiten out the mess they made of their lives or something like that. Also there is some BDSM elements where the women gives him lessons on being a master like giving and receiving discipline like spanking and whippings since she is a fairly well known member of that community and notices he seems interested in the lifestyle if not to the level she is.
I hope that helps in the search and hopefully I'm not mixing several stories together as I'm a voracious reader for example SOL has 41K+ stories and I read 23K+.