lead a double life

To keep part of one's life hidden, especially a part that would not be approved of. For years, he led a double life, shacking up with another women while his family remained in the dark about everything. The movie is about a mother and father who lead a double life as secret agents.

Live as if one were two persons, usually one good and one bad. For example, They learned that his frequent travels were actually fictitious, and he was leading a double life, with a second home on the other side of town . This phrase is frequently used for a married person who establishes a second household with a lover. [Late 1800s] Also see Jekyll and Hyde.