Conclusion
Being alone and being lonely are two entirely different things. When you are alone, you are physically not around people but when you are lonely, you are emotionally disconnected from people when you are around them.
People who are lonely tend to pick bad habits to numb out the feeling. Most of them become drug addicts and alcohol abusers. Loneliness can affect you and lead to the development of physical and mental disorders.
There are ways you can help yourself if you feel lonely. You can also seek help from a professional health worker if your case is severe.
References
[1] https://en.wikipedia.org/wiki/Solitude
[2] https://medlineplus.gov/druguseandaddiction.html
[3] https://www.nhs.uk/conditions/insomnia/
[4] https://www.mayoclinic.org/diseases-conditions/anorexia-nervosa/symptoms-causes/syc-20353591
[5] https://www.mayoclinic.org/diseases-conditions/anxiety/symptoms-causes/syc-20350961
[6] https://www.nimh.nih.gov/health/topics/depression