hi, it is fair to share this burden with someone you trust. his brother is his blood, and it may help you (words) for you or even for your boyfriend. it will be difficult for your boyfriend not touching coke, because he sees everyday these coworkers, he has the same habits.
It is a fight for him and for you. if he loves his job, why don't find the same job elsewhere (on in the same town) but preferably far from the actual work?
good luck!!!!God bless you.