Being alone and feeling lonely aren’t the same. You could be mostly isolated from the world around you and feel fine. You could be surrounded by people but feel lonely.
You still have at least one person who cares, and that’s great. Some people have more, others have fewer. The number doesn’t really correlate with how you feel, because people don’t need the same amount of social interaction. Apparently, you would prefer more, hence the loneliness. How about a social hobby of some sort?
Anyway, this may also explain why other people didn’t bother saying goodbye. Maybe they don’t feel lonely at all.