keep to oneself
Also, . 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.
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