I am sorry you are going through this.
How often is he using or aren’t you sure??
why doesn’t he want it in a shared account? What’s his rationale?
sadly I feel (from experience) if he is an addict every Penny of his money will go on that. I have a sister who is an addict and she stole all of her children’s savings and my dads totally what we counted at least 10k prob more just to get her fix every night!
I also have a now ex partner who spends all of his wages on crack cocaine.
from personal experience . no you aren’t being unreasonable at all.
you have reason to worry!! Xx