King, I am sorry about your dad and I know how you have struggled with this.
Sadly, he will use or not use whether you worry or not. Until he is ready to quit, nothing can change his course. Believe me, if love and trying everything we know could stop an active addict, not one of us would be here.
My son is an addict so I know your pain of watching someone you love destroy themselves. We don't have to allow ourselves to be destoyed too, King, and what helped me more than anything else was to go to meetings, get a sponsor and learn to work 12 steps of recovery that literally saved my life.
There are meetings where you are, maybe try to find one and give it a chance. You have nothing to lose and everything to gain.
My prayers go out for your dad and for you too.
Hugs