This was me back in March after 10 years of use.
Typical behaviour stuck in a cycle. If he wants to stop he needs to write a plan out.
Get active. To do this he needs to go a week without use. Plenty of fruit juice and multi vitamins.
The next 10 weeks of his life will be held his behaviour will be erratic. The depression gets worse and anxiety goes through the roof.
If he’s adamant about doing it you need to get him active and he needs to want to stop. If he has debts with dealers make him pay them but you pass the money over so he doesn’t pick anymore up.
It’s hard to do it really is but the cycle needs breaking.
If he can get to 14 days with no use it becomes so easy to do but in all honesty what your telling me he isn’t ready to stop yet so you need to make a decision. Only he can help himself no one can drag him out it’s all on him.