How do I stop my friend from giving me all his money?

I heard giving away money and possessions is what a guy does when he's suicidal, so maybe this is a bad sign - plus he told me he was severely depressed and that he was "finding a way out", but I figured he was just a little sad and that he'd just snap out of it like how depressed people normally do. Anyway, he asks me for some of the money back because he gave me A LOT of money, and he says he doesn't want to die exactly but he hates living especially if he doesn't have money. How do I help him without returning his money? I reckon I should take off now that I've got his money.

For now, I'm not taking any more from him because I'm a great guy, and I'm looking out for his wellbeing because I'm an excellent friend. The problem is that he wants to give me even more, unless I return some back. He describes it as like the gambler's sunk fallacy, whatever that is - I don't know, maybe he gambles.
How do I stop my friend from giving me all his money?
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