I can relate. My deadbeat relative is my oldest son. There is no end to what a family member will put other family members through. My strong advice is to provide nothing more or less than what YOU are comfortable with, on this one your wife has to yield to your judgement. This is a potential bottomless pit. Stay away from the edge and do what you can to cut that tie. Tough love really is tough on everybody. I feel for both you and your wife. Good luck.
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It's all downhill from here. Except the parts that are uphill.