Lay down arms.

Put the child first.

Your child needs both parents to be happy and healthy, so go to therapy and help the mother get the help she needs to be sober and well for your child. This is the only way to approach such a situation, I was a child of such so I know.

I loved my mom, she was the best, but she had addiction issues and I suffered, but my dad did the right thing and we all helped her, and I was better for it. If I had not been able to be in her life, it would have been awful, and I totally forgive any and all that went wrong.

Put your petty differences aside, or you will be paying attorney fees forever that could and should go to your kids future and wellbeing.

Accept the relationship is over, there are no winners here, this is the death of a family and the child is the one who suffers forever from it, you two will move on to new relationships and be glad you did.

If you make peace now, you will give your kid the edge they need to be a child of divorce. If you make a war, your kid will be screwed for life.