There's a difference between being alone and being lonely. Being alone means there's no significant other to wake up next to, to call when we get good news, or to kiss goodnight after a long day. Being lonely means living perpetually in a world not being able to escape ourselves and craving anything but our own company.
Every one of us will experience loneliness in our lifetime. It may hit us when we're single and spending Saturday night on our couch watching reruns or when we're smack at the center of a packed and pulsating party. There is one clear reason for this, and that is that loneliness is not just being alone, it is a perception of seeing ourselves as alone.