You pretty much have to be there for him . . well obviously . . It will be good to spend more time with the guy, talk to him, and hopefully to be able too encourage him. Nothing is of more value to a person than another sacrificing time for him or her to be honest. Be wary though, suicide attempts normalyl spell out a very deep root and can be extremely difficult to handle especially when you are trying to help such a person. Even kind words can be easily misinterpreted, and as such you ahve to be very very sensitive towards them. Is you're not very close to him, its a risk, but love from the heart usually never fails.
Be there for him, and let him know that you are with him regardless of what happens. Let him know that he means SO much to you.
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The key to victory is the element of surprise.
When that doesn't work, I guess I just gotta gun you down.