First of all, it’s not your fault that he became addicted to opium during your separation. Period.
He is likely drinking and/or drugging far more than you know, so I would not let him take your son with him as he is driving while intoxicated. This is a disaster waiting to happen.
Go to the friends and family forum and read and post there (perhaps this post will be moved).
Go to an AL-Anon meeting! You need the support.
Wishing you all the best.