He has gambled most of the rest away. Always needs some poor soul to live with him and ends up taking his money. Currently a woman 30 years younger than him who he is having sex with wants to move in with him and take the rest. He is physically healthy and is losing his mind yet his lifestyle and choices make it difficult to intervene.
In some cases, social services can help out, but it's not likely if no one is breaking any laws and he's not being abused. I know it's hard for you to watch, but until he is in such a cognitive state that it's obvious he can't make decisions, you may not be able to intervene. Even at that point, you may have to go to court for guardianship. This is a tough case for you. I'd suggest Al-Anon meetings to help you cope. You'll meet others who understand.
Carol