I agree with most of what you said, but that path isn't just a fetish. For me, Mary was the best one for the NTR option, because it represents the extreme regression and essentially falling back into the dark pit forever after being given a glimpse of the light. As the mc, the choice was yours to pull her out fully and be her shield or fall in with her.
I certainly could've written it better as I do not claim to be a particularly good writer, but I feel the concept is still faithful to Mary's theme.
Anyway, that's the last thing I'll say. Appreciate the insight!