You can feel lonely amidst people, and you can be home alone. So one is in the mind, and the other in the body..
One can be happily alone but not happily lonely
You can be lonely in company but cannot be alone
lonely is by yourself or feeling detatched from others. being alone is simply physical, not emotional
Alone is a state in which you are by yourself.<br />
Lonely is a result of that state of being alone.