I have not experienced your situation.
What I can say is that I tend to look for ways in which my AW can "prove" to me that she's on the right path. This doesn't work and it drives me batty.
So reading your story, I see you trying to balance his cheating and drug use with removing his FB contacts, or removing the text contacts, or whatever else. All that stuff is chump change compared to cheating and using.
Take care of yourself. If you keep worrying about him, you'll be lost and your child will be next.
Edit: Eventhough, I've imagined it, I can't imagine what it would be like to be in your shoes. Keep on posting. It really does help.