observanteen raises a good point. Chayecha kodmin – the first order of business must be to keep yourself safe. If this requires limiting the amount of time/effort you put into your brother or friend, so be it.
rikki77, I know others have said this, but it’s worth repeating: find yourself a Rav/Rebbitzen who you can confide in and connect to, to can guide you. Then he/she will be able to judge the exact circumstances and personalities involved, and show you the most effective path for both you yourself and how to help your brother.