Welcome. You will get quite a few responses I'm sure, but you may not like the responses you get. Your father is an enabler. I am sure he truly believes he is being a loving father by helping you out financially. I am sure you are grateful for his generosity. But it's enabling. You're right that schoolteachers are underpaid. (I know that from having worked for the president of a teachers' union.) However, there are schoolteachers who can live on their salaries. Although some areas of the country pay less than others, there is a high demand for teachers, so they can move to areas where the pay is better if they so desire.
So your father is an enabler and appears to have passed that trait onto you. It sounds like your family as a whole is trying to give the addict in your life plenty of love in the hopes that he will respond positively. I does not work that way.
Addicts do not consider other people in the equation when it comes to their addiction. They, and they alone, own their addiction. And as far as I know, nobody has ever been born who can control an addict or any other person.
You can continue to try to rehabilitate him and make him see the error of his ways, but I'll guarantee you this: if he wants to pick up, he will. And you and your family will not factor into that one simple equation. He has to want to beat the addiction all by himself. Sure, you can be supportive and loving, but you need to detach. He is messing with your money; money you claim is in short supply unless your father helps out. Maybe it is time for everyone to step back and let the addict find his way back to recovery.