We are in the same situation as you. My son (now 5) and I have never seen him sober since my son was born. My AH is addicted to cocaine, marijuana, alcohol, steroid pills, gambling, escorts, porn... you name it. My son and I deserve better and I want you to know that you and your child deserve better too.
The hard lessons in life are meant to make us stronger and while they hurt like hell, your decision to move on without your partner is the greatest gift that YOU as a mother can give to your son. Trust and have faith in that.