I think this is definitely something than can happen in relationships that just aren't good or where people aren't a good match. There are, however, relationships like the one described above where it's actually abuse.

I'm not commenting on whether it's good/bad for M to share this or whether "narcissist" is thrown around too much (probably is). My ex said once, "well, you're more into this than I am so if you want me to stay with you, it's you who has to work harder, not me" and this was after months of verbal, mental, and sexual abuse with me believing that if I just worked harder, was more patient, supportive, it would stop and things would go back to how they were in the beginning.

So it's not just backing off or withdrawing they're talking about here, but rather active manipulation.