keep to oneself

Also, keep oneself to oneself . Shun the company of others, value one's privacy, as in She kept to herself all morning , or, as Doris Lessing put it in In Pursuit of the English (1960): “She keeps herself to herself so much.” [Late 1600s]

Refrain from revealing, hold secret, as in He promised to keep the news to himself . Also see the synonym keep under one's hat .