My ex wants visitation with our 7 yo child but he has history of dui. I know he is still drinking and doping cause I smell it when I see him. I allowed him to visit our son as long as it does not involve driving a car. Now he threatened me to go to court so he can have custody that includes him to drive my son. It scares me to death because I know he is going to be drunk and going to put my son in danger. Please help me what should I do. I have no money to pay a lawyer.

You can try but most likely he will get court ordered visitation, You may ask for the exchange to happen at the police station, so if he is "drunk" the issue can be seen first hand.

But while a valid concern, normally unless there is some current proof of problems, he will win and get visits though court.

You can ask that visits be supervised.