I don't understand this perspective at all, @sarahsweets. What did he do to take advantage of her? It actually sounds to me like he was very generous except for the interest thing. I've had wealthy family members loan me money with a similar interest rate and I didn't think I was being taken advantage of. Wealthy people are wealthy for a reason: they are smart about managing their money.

And otherwise, to be perfectly honest, dealing with someone who has this many mental health issues is not easy. I just don't see abusive behavior in what the OP describes.