Hey @Sally95 that sounds really tough, it's so hard to watch our loved ones experience distress and trying to help can be so challenging. Posting here shows that you really care about your brother and you want him to be ok which shows you are a really caring sibling 
There is some information in this article that you might find helpful, it is about supporting a friend (it is applicable to family members as well) with drug issues.
It gives some tips about how to be a supporter such as not guilt tripping and letting them know you're there for them. It's also got some links to services that you might find helpful.
Supporting someone else can be really difficult and it's important that you are able to get support for yourself if you need it, for example contacting Kids Helpline for some one-on-one counselling if you think that might be helpful. What are you doing to look after yourself in this difficult time?