Most Helpful Guy
Except the drinking everything sounds normal
Most Helpful Girl
Now this is my opinion just from the outside looking in. He is not a good force in your life right now. By that I mean is he dragging around a lot of negative energy a girl like you does not need at 19. problems with his dad and his drinking problem are just the start. You said it yourself that you are scared at times. Is that any way you should feel if you love a guy.
Now the whole cocaine/trouble with the law thing is an entirely different monster. A more evil one. That could also get you in trouble as well.
What if you were driving with him, he gets pulled over, the cops find coke and he blames it on you?
He is 6 years older than you. He needs to figure himself out.
Read this part carefully: You are NOT obligated to fix or help him. Please please focus on you and where you're going with your own life and if you do not feel safe please leave the relationship.