If your H actually participates and continues to get support and help regarding the M "problems"...
Would you consider that he is "working on the M"?
Have you decided what you want, yet?
Yes, I know you are here and want to work on the M and I know you have suggested such, although it still appears you maintain your position of keeping the M intact only until your S graduates...
You continue to have a few choices and none of them are easy:
+ Actively work on yourself to help make the M better + Continue to "survive" the M until your S graduates + Consider that your M actually is already dead and continue on with D
Personally... I think the second choice is the easiest route...