I'm sorry that you are in this situation. Just know that there are many families who may look neat and tidy on the outside who harbour a lot of family dysfunction.
There is nothing you can do about your dad's situation. Just focus on you and your school / work. You aren't a child anymore and do not need to be living at home, so it's your dad's house and he can do what he wants in it. If he chooses to drink, that is on him. All you can do is have a heart to heart discussion (when he is completely sober) and tell him how you feel without blaming. It's up to him whether he chooses sobriety or go down the path of his own father.
It's good that you are in therapy, good that you joined us, the more you are educated in the topic of alcoholism and codependency the better. Statistics are high for daughters of addicts to end up marrying someone like their father and therefore having a horrible relationship as a codependent. It's great that you are beginning to take measures now at 19.