loner
n.someone who prefers to be alone rather than spend time with other people. You use this for a person who does not have many friends or does not want them.
n.a person who avoids or does not seek out the company of others. Often carries a neutral or slightly negative connotation depending on whether the isolation is perceived as a choice or a social failure.
“He was always a bit of a loner at school.”
“While his colleagues went out for drinks every Friday, Mark, a natural loner, preferred to head home and read.”
“The protagonist is portrayed as a stoic loner whose self-imposed isolation serves as a defense mechanism against the emotional demands of his community.”
Often used with the verb 'to be' and the indefinite article 'a'.
From lone + -er.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.