This site just posted an article about it!

And in this article the case is MUCH worse (think rats, dead rats and live rats, yes, rats).

So maybe send the article to your fiance with a preamble along the lines of: "of course this is a much tougher case, but..." and that would restart the conversation about his mom.

Here is the link:

The Hoarder Next-Door | Amazed by Grace