Lonely
adj. 孤独的, 寂寞的，荒凉的, 人迹罕至的
It describes a feeling of sadness stemming from isolation or abandonment.
它用来来形容一种因孤独或被遗弃而产生的悲伤情绪。
例：
The lonely old man was much to be pitied by all of us.
那位孤独的老人得到了我们大家的同情。
A person can be alone without feeling lonely, since alone describes a state of being and lonely describes an emotional response to one’s circumstances. Most people don’t feel sad when they go to the bathroom by themselves, for instance.
一个人可以alone而不感到lonely，因为alone是一种状态，而lonely是对一个人处境的一种情感反应。例如，大多数人独自上厕所时并不感到悲伤。
Alone
adj. 单独的;孤独的;独自的
adv. 独自地;单独地
It describes a single person or object, separate from others. One who is alone is by oneself.
它形容一个单独的人或物体，与其他个体分离的状态。如果一个人是alone的，就是说他/她只有自己。
例：
She went to the movies alone, because her friends talked too much.
她独自去看电影，因为她的朋友话太多了。
Emma realized that she was alone in the desert.
艾玛意识到沙漠里只有她一个人。
As you can see, a person can be alone in the sense that no other people are present, or alone in the sense that he or she is unaccompanied, even in a crowd.
一个人可以是其他人不在场的时候alone，也可以是没有人陪伴的时候alone，即使是在人群中。
最后总结一下
❖ Alone describes a state of isolation or solitude when one is outside the company of others.
Alone指一个人在没有其他人陪伴的情况下，处于一种孤立或孤独的状态
❖ Lonely describes a feeling of sadness or abandonment.
Lonely是一种悲伤或被遗弃的感觉。
Loneliness is often, but not always, a result of being alone.
孤独(Loneliness)往往是独处(alone)的结果，但也并不总是如此。
