Another mom of a heroin addict here. My son is 24 and currently in rehab.
I can totally relate to your comment and your son building walls and thinking he can handle this. Exact same story with my kid. He didn't, and still doesn't want us too involved in his program (not a bad thing). I know he considers asking for help to be a form of weakness and is embarrassed about his situation even though he tries to hide it.
I agree with the comment that this situation creates PTSD in parents. Please take care of yourself. I still suffer from insomnia after not being able to sleep for so long because I was afraid he was dead.