Have you tried putting all your attention to the present moment? By that I mean being aware of the thoughts in your head, being aware of the feelings inside your body, being aware of everything you sense. Being fully aware results in a complete halt in thinking. Be aware but don't try to think.
I believe the mind is your enemy. Not you. Postive & negative thoughts are pretty much the same thing. It is the mind that separates them to thoughts you want to avoid and thoughts you want to keep. The mind is putting you to brink of suicide, but you need to remember you aren't the mind.
First step I suggest is to listen to the voice in your head. Just listen, just be aware of it. Don't judge, label as negative, the voice. Just listen. Stop thinking and listen. It can be difficult, but the solution to all this is to be aware of the mind without using the mind itself.