elizabeth,
I am not an alcoholic and I'm not rich and I wouldn't justify as your dad did (not talking to "him"). I don't loan money to a family member without a legal contract.
My children know this and I think it is a plus for them to know that I am not their personal bank to bail them out of their own problems. I have made loans to one son only because he writes up the contract and we discuss it in a business like fashion.
I am sorry that you are learning the hard way but sometimes it is the best way.
Hugs,
Loulouise