I had a dream that your friend killed himself what does this mean?

Most often, a friend represents the dreamer's own self. So this dream could express some underlying depression or desperation. BUT, if the dreamer is certain the dream is not about the self, it is possible that the subconscious mind has picked up on subtle signs of the real-life friend's depression. In either case, reaching out to the friend would be appropriate, and helpful to both parties.