hello there.
I am sorry that you are in the midst of such confusing heartache. Addiction is just so powerful, cunning and baffling. It is so so so hard, as the one who is not addicted to the substance, to understand how anyone could choose a drug over their wife, their child, their life.
It is going to be really hard once you come closer to the deadline that you have set...you have drawn a line, you have stated a boundary. I used to try to draw these lines. I would say them, it would be a threat I would make, an ultimatum. Addiction does not usually respond all that well to ultimatums...so be prepared for that.
It can and will be baffling if he can not behave in accordance with your boundary.
It seems from your post that you understand that it must "come from him".
Your own test is going to be that your limits, your boundaries are going to also have to come from within...you. I found that with my ex I had to finally uphold my own boundaries...they finally came from within and were about me.
I decided that I could not live with active addiction.
You will need to decide for yourself what your boundaries mean, and hopefully those boundaries will work best for all involved, especially your child.
I do have faith, I do believe that when you are living and doing what you need to be doing, what is best for all...then life shows up to help. Although he is involved in caring for your child...if you end up needing to decide that he should not be doing it...I do believe that somehow life will show up to show you the way.
Setting healthy boundaries for yourself and your child invites a healthy lifestyle to grow around you. Praying for you...