keep to oneself

verb2

1. •
   To refrain from telling or giving; to keep secret, or refuse to share.

   • Then he fell to gabbling strange and dreadful things which were not clearly understandable, and which the doctor admonished them to keep to themselves. — 1900
2. •
   To purposely avoid interaction with others; to be introverted.

   • She preferred to keep to herself after her husband died.