It seems to me like gregarious people and loners can be after the same thing. Some people want acceptance and approval from others whereas other people have more of an inner connection to the same source.
What is the source? We don't understand (yet) but it's an interesting clue that the things other people like about you aren't necessarily the things you like about yourself.
> Needing to be alone after school or work is not quite the same as being alone 24/7 for months.
Yes that is a different kind of solitude, this is more of a distinction between people who are part of society but with minimal social interaction, and those who seek maximal interaction and have some kind of dysfunction without it (e.g depression).
I'm more part of the former group, I don't usually seek out social interaction but don't shun it either. I enjoy interesting conversations with people but I never feel lonely in their absence. I suspect this may have more to do with what else fills a persons life, rather than some deeper psychological difference (or some crude dichotomy such as introvert vs extrovert as many probably attribute it to).
We are totally dependent on others to feel good. It is how we are wired as social creatures. Every single person, without exception, begins their life needy of another's approval and attention. The attention of others is how we construct ourselves.
Over time, we lose part but not all of that need, in different ways, depending on the interpersonal dynamic with our parents. A healthy person's end result is a healthy balance of dependence: too much can be limiting to a person's own agency, while too little means a miserable, lonely existence.
It's not weak to be dependent on others. On the contrary, it requires emotional strength — a strength which is built. Typically by families, but sometimes by close friends, caregivers, or significant others.
This makes us incredibly week as well, totally dependent on others to feel good.