Question

What is the difference between being alone and feeling lonely?

Answer 1

There is a great book on the US society in the sixties, "The lonely crowd", in which the author laid out the case that folks could not relate to others except through material comparisions...salary, yard, home, wife. Because they couldn't relate to others, their ability to understand themselves was inherently a lost cause: lonely even when in a crowd.
http://en.wikipedia.org/wiki/The_Lonely_Crowd

being alone means being without company. Being lonely is being without soul mate, a confidant, and understanding their needs and your own.

A sad life.

Answer 2

Being alone is a neutral state. It says nothing about the feelings of the person who is alone. Personally, I relish being alone sometimes. I can think my own thoughts and do my own things.

Loneliness is a feeling. Lonely people miss having human companionship and are sad that they are alone.