You can't save him or make him stop hurting himself or attempting suicide. All you can do is offer to be a support person if he wants help. Offer to call a hotline with him or sit with him at the hospital. You can't force people to change, but just being a stable friend is a gift for many people struggling with mental illness. You can always call for a welfare check if you're worried he has taken something or plans to but that's the best you can do.