I definetly have some for of social phobia, I have a very small base of friends and the only reason I stay in contact with them is, 1 I live with, the other I have on msn, and the other is my gf and we have children together... I find social situations exhausting, and I hate the anxiety that comes when confronted with annoyance and shallow people.. but I got thinking that maybe its my approach of where I chose to go, so I am gonna try a yoga course once I can scrape together the money to do so. There have been times I was invited to a social outing, and I intended to go, even got to the location then feeling totally unable to get out of the vehicle, even thinking about going into the place I felt like vomitting all over.
I do think isolation can increase a suicidal persons ideation of suicide, but I dont think it is the root cause for most people.