Good intention of course, but bad mistake. You should have referred him to mental health help and stayed out of it. You have now involved yourself legally. I know, crappy but reality. This won't be last to time this happens with this individual and you could get caught in both a moral and legal mess. Personal responsibility is necessary and anonymous intervention from some mod or admin can be the wrong kind of intervention. Put a link to a suicide hotline on your forum.
http://www.suicidepreventionlifeline...rsButtons.aspx