I've seen this kind of scenario before. Don't let circumstances bleed you dry. Take decisive action to clear up the financial questions and go to a judge/lawyer if that's what it takes. Keep records of every dollar that goes anywhere, evidence of infidelity, etc.

You can always decide to be more generous later, but let that be your decision, not hers or some disinterested third party that will assume that you went on living this way because you consented.