withdrawn

Quiet loners are withdrawn — that's a word for people who keep to themselves to such an extent that it seems a little unhealthy.

We can all be withdrawn sometimes, especially when we're sad or depressed about something. Some people get withdrawn when they're angry. A withdrawn person can be hard to find, and even if they're around, hard to talk to — withdrawn people don't like to talk, or they try to talk as little as possible. A person who is withdrawn from the rest of the world for a long period of time is a recluse — an extremely solitary, withdrawn person.

Definitions of withdrawn
1

adj tending to reserve or introspection

Synonyms:
indrawn
reserved
marked by self-restraint and reticence

adj withdrawn from society; seeking solitude

Synonyms:
recluse, reclusive
unsocial
not seeking or given to association; being or living without companions