This post has content warnings for: mopey, cringe, and self-indulgent.

Absolutely. I think there is a certain kind of person who surrounds themself with people and still feels lonely, and maybe solitude is an important step to getting past that, but the cure in the end, for everyone i think, is to be around people who love you well and whose love you can accept into yourself. I think that's the only real remedy
Loneliness is being alone and sad, and solitude is being alone and happy. They're kinda two different things, IMO, and the key is not your situation but how you react to it (you can be happy or sad, whether alone or not, for many reasons).
You can absolutely be lonely or have solitude while surrounded by people, also