A long time ago I was the one sending messages to people I knew, telling them I'm going to hurt myself, which I eventually did. I survived it and when I think back on all the people that didn't respond or ignored me outright, I can't blame them. I actually understand. People have to look out for themselves and their families, and sometimes that means keeping unhealthy people at a distance. On top of that, my choice to do whatever I do to me, is my responsibility, no one else's. That can be tough to accept for the ones on the outside of the situation, but for the one in it, dealing with it, they ultimately need to save themselves. That doesn't mean they can't receive help, and I think you calling his sister is about the best thing you could do. Hopefully he gets professional help for this because that can do a lot to transition a mindset like his to something brighter.