B1
unhappy because you are not with other people
Dictionary examples:
The lonely student taught math to his teddy bears. (0.0)
The lonely boy built a robot friend from old boxes. (0.0)
The lonely astronaut talked to his plants on Mars every day. (0.0)
the lonely life of a farmer (21.2)
She gets lonely now that all the kids have left home. (36.8)