Loner

The Sims 3

Loners enjoy time spent alone more than time spent with others. Quite shy, they will never approach anyone that isn't a close friend. They prize their solitude and get nervous around large groups.

The Sims 4

Known as Loner in this game.

These Sims become Happy when alone, do not receive negative Moodlets when their Social Need is low, become Tense around strangers, and become Embarrassed more often by social rejection.