What blows the absolute and utmost about suicide is that, when someone really wants to take their own life, it can’t be prevented save for someone finding said person in the act or directly following and then maybe not even.
The most help you can give is to be a friend.
If you fear for a friend or family member’s life, make sure you let them know how intergral a part of your life they are; my mom saved me that way since I knew she wouldn’t survive me killing myself.
Be a thorn in their side.
If they draw back into themselves and cut everyone out, bug them. Text them. Email them. Call them. Show up on their doorstep with Chinese and force your way past them if you have to. Make them focus on something other than their pain.
When my father tried to commit suicide, I was over six hours away. Luckily paramedics were called by someone who saw my father in a ditch. Your friend might not be so lucky. If you think your friend is going to try and hurt themselves, forget about how angry they will be and go with your gut.
If you can stop a suicide attempt, know the war hasn’t come even close to being won. This battle, this one right now at this very second, has been won but the war? The war is still there and you can’t win it; it’s not your war to win.
If you can’t stop a suicide attempt, know it was never your war to fight. Know it’s not your fault. Know you did what you could with what you knew and even if you had known more, it might not have helped.
In the very, very end, the result and blame/congratulations, lie with the one who is fighting the battle with himself.