Hiya Blue eyed,
First, I want to welcome you to Sober Recovery. You have gotten yourself to a good place to help you sort out all these emotions you are currently going through.
The problem is, there is truly nothing you can do to help your step brother stop using drugs, You CAN let him know how much you love him but beyond that, he needs to seek help for himself....when he is READY.
As for him being suicidal. If you feel he is a harm to himself and others, do not hesitate to call 911, or call the police.
There are alot of family members, in the same situation as you are on the nar-anon board, so feel free to post over there if you would like.
I'm glad you're here.
Hugs coming your way.....