Welcome to SR, Firstlight.
My son is the addicted loved one in my life, so I know your pain.
The line you draw has to be the line that is right for you. For some of us it is no contact, although that is harder with a child. For others, we may meet our children for lunch or brief get togethers (whether they are using or not) and not get drawn into the drama.
My son is lost in his addiction somewhere, we know not where. But my line is drawn that he can contact us if he is clean and working a program of recovery and preferably has been clean for some time as he has been in and out of that revolving door for many years.
The thing is we cannot control their choices, no matter how bad they may be. But we can control how much we let their choices affect us. That's what recovery teaches us, how to find peace no matter what our loved one's choices may be.
Hugs