Looking for a story (tentacles, kinda dark)

I ran across a rather dark story about a young woman who had discovered some sort of entity, tentacles and such, that provided great physical pleasure in exchange for degradation and declining physical health. Despite the fact that it was slowly killing her, she kept returning. It was almost a tentacled metaphor for heroin or something. In the story, there were other women who had done the same, eventually either dying or vanishing with the entity. I remember it was in a basement or something, and there was some creepy old man who witnessed all of it.

A very strange, dark tale that was haunting and well-written. Does this ring any bells?

Source: reddit.com/r/sexystories/comments/6rny8o/looking_for_a_story_tentacles_kinda_dark