Autophobia is the name of the anxiety disorder for one who fears being alone.
Other words that may describe a person who doesn't like to be alone:
claustrophobia
Monophobia
Trypanophobics.
Acrophobic
Lintophobic.
A person that is afraid of the dark has a nyctophobia
Sensible or a pyrophobic.
Hermit!
demophobic,androphobic
Hermit
Social Anxiety?
I'm afraid not Nope new person :(
I would call it common sense. PS: there is no phobia around that, isn't everyone sorta afraid of that?
afraid to open up