I'm really worried about my dad and I don't know how to approach this. He's in his 80's and he's gotten obsessed with a woman in her 50's (younger than me) and she's taking him for thousands a month. He is also blowing off family events and celebrations to spend time with this woman - even missing a family funeral! Whenever anyone tries to talk to him about her, he gets furious, screaming and refusing to talk. She is taking him for huge amounts of money - hes' even given her a credit card that she uses with no restraint. Not only is he destroying his finances, but his destroying his relationships with everyone else because of her. I don't know how to get through to him.
With a lawyer
If he wants to deny what is happening you won't stand much chance otherwise
Have you spoken with her about this?
She needs to know that the family is aware of your father's generosity to her - and she should respect limits on her spending.
Try contacting the family lawyer (if he has one. There's not much you can do except to get guardianship of him, which will mean you take over his financial affairs because he is not able to. That will take a Dr.'s verification that he is not able to make good decisions for himself.
Speak to his medical Dr. about what is happening, too.