No. You can be happy alone. But 'lonely' suggests you are sad that you are alone.

To be alone is simply to have no one around you. "Lonely" is a feeling - "to be lonely" could equally be "to feel alone". If I like being alone, then I'll never feel lonely. If I'm in a crowd of people don't feel like I belong with them, then I might feel alone (even though I'm not actually alone) i.e. I'm lonely.

alone = on one's own lonely = feeling of sadness about being either physically OR emotionally alone Although you can be both at the same time ("feeling lonely while you are alone") and sometimes people assume that those who are alone are also lonely, the words have different meanings. You can indeed be happy while you are alone or lonely in a crowd (surrounded by many other people but not feeling like part of the group). Introverted people enjoy spending time alone/away from others for long periods of time, but that does not mean they feel lonely. I hope that helps and isn't more confusing...!

Lonely is a feeling or emotion. For example, "I went to a new school today and felt lonely because I didn't know anyone". Lonely can be a similar feeling to sadness or missing someone. Alone is when there aren't any other people around. For example, "I was at home alone for three hours" means you were the only one in the house for three hours. It's certainly possible to feel lonely when one is alone, but that's not always the case. One can also feel happy, relaxed, etc. Hope this helps!