I'm sorry you and your son are still dealing with this person's relapses and chaos.
No contact is always a good choice in such a situation.
What kind of therapy / support is your son getting on a consistent basis?
It seems that he has been exposed to this for most of his young life.
As I posted on another thread, this kind of exposure led to life-altering negative consequences for me as it does for so many COA kids.
Please do not underestimate your child's need for support--on-going
Being on the road, no permanent address, no "safe zone" must so stressful for both of you, but kids in particular need a safe zone and some predicablity
in their lives.
I never knew what was next as a child. Sounds like this may be the case for your son also.
You as an adult may be able to handle this far more easily then he.
Remember, kids quite often "fake" being OK so as to not rock the boat and to reassure the adults around them. Especially COA kids like your son.
Please be well and perhaps this may be a signal from the Universe that you should consider not letting your addict in your family space for a good long time if ever.