It is disappointing that when W dropped the bomb she said she would give the M 6 months to see if things improved. You DB'ed your heart out and she didn't/couldn't acknowledge the changes. There's got to be some reason she wouldn't/couldn't acknowledge your changes. The reasons that come to my mind are: OM, mental health problems, lack of concern because she knows her parents will support her (if the latter was the case, wouldn't she have left before now?). The changes to the dynamic that you are considering (i.e. separate checking accounts, asking W to move out) may give you more insight into what is causing her to be so rigid in her thinking.
These changes may be what she needs to wake up. Of course, as always, you are doing what you need to do to be healthy and you will proceed in a thoughtful, rather than destructive, manner.
It will be interesting to see if she already has her contingency plan set up.....That should give you a sense for how well-planned her exit is.
