The point is not whether or how long H should provide financial help to his children. But rather that he needs space to make those choices on his own without it saying something to you about his love for you or commitment to the M.
One way to do this is to separate finances. It might take professional financial help as well as counseling to figure that out. Or, it might be as simple as choosing as agreeing for you each to have discretionary spending accounts.
The important thing is to really examine the behaviors around financial matters, understand them. and choose something different. It sounds like you are trying to fix H, control his choices, use his choices as a litmus test, and manage his R with SD. Better to work on yourself and with your H on your partnership.
If you resent the choices you make about your money, make different choices. Get your own financial advisor. Figure out what you need to have the financial stability you seek as an individual and as a couple. Own it. Make it happen for yourself.
For your M to be healthy and happy, the dysfunctional dynamics around finances need to change. You own those as much as H. The difference is, you can control your contribution to that dynamic, but not his.
FWIW, I agree that is is much healthier for SD to become financially independent. My SD thought she'd get a free ride from us (room, board, tuition) at age 23 or 24 through an MA program. When she learned that we would reimburse only a significant percentage of tuition after each successfully completed class, she totally lost interest. Instead of pursuing an MA in an area to which she was not personally invested, she instead took an entry level job in a field for which she had true passion. Five years later, she is incredibly confident and successful, has her pick of jobs, and makes very good money. Had she coasted as a dependent child for another few years and graduated with an MA that she really didn't care about, she'd be in a very different place.
