Sandra Bullock's husband Jesse James cheated on her with other women besides tattoo model Michelle McGee, multiple sources tell the new Us Weekly (on newsstands now).

"This is just the first person who has gone public," one source tells Us Weekly. Adds another, "This is not an isolated incident. When Sandra is away, he gets bored."

In fact, James' infidelity has been an open secret among employees at his West Coast Choppers bike shop in Long Beach, Calif.

"Everybody knew," one source tells Us Weekly.

James, 40, would regularly post Internet ads looking for "hot, tattooed biker chicks with big boobs," says a source.

Adds another, "He sees their photos, answers the ads and invites the girls to his office."

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How could Bullock, 45, be in the dark about her husband of nearly five years?

"He is a whole other person when they're together," says a source.

Adds an insider, "She was completely duped."

For more - including how Bullock remains "completely sealed off," the cruel way James demeaned his marriage to Bullock while wooing McGee, whether Bullock will take him back and shocking details on James' disturbing Nazi connection - pick up the new Us Weekly today!