It seems like the choices we're presented with are sorrow because we have no friends or sorrow because the friends we had have gone. Nostalgia over good times past can sting even when those same friends are still around. Suffering is an integral part of life--maybe the main part.
What's strange then is that the mind gravitates towards pleasant memories at all, instead of exclusively on bad ones. I suppose it only fixates on happy times when doing so causes sorrow. There's just no escape from it.