It could be strong introversion or Autism.
Not knowing your emotions is a sign.
It is important why it was so difficult for him to socialize. If it was because of just did not like socializing or because he has difficulting understanding others motives, or just does not have the innate social skills most others have?
Does he not like socializing because he finds the noise or the lights, or the smells exhausting?
Does he have some sort of unusually intense interest or repetitive behaviors?
Most people have a few of these traits to some degree. Many other conditions share traits with Autism. If you are autistic you have most of the traits to a degree that is life inhibiting or at least makes life very and constantly exhausting.
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Professionally Identified and joined WP August 26, 2013
DSM 5: Autism Spectrum Disorder, DSM IV: Aspergers Moderate Severity
“My autism is not a superpower. It also isn’t some kind of god-forsaken, endless fountain of suffering inflicted on my family. It’s just part of who I am as a person”. - Sara Luterman