Sometimes a woman may not be aware that the person she cares for is taken. If she is aware, she may already be in love with the man. Love will make you do foolish things like believe the lies " I am leaving her." "I love you." "I am divorcing her." which he may be telling her. She could also be in denial and believe that she can "take/steal" the man from his mate. Basically, their is many reasons a woman will put up with the behavior.