I hate my fiancés mom !

This lady boils my blood , she hates me because I'm not the person he was previously in a relationship with , he has a child with a very bitter woman from a previous relationship and she absolutely loves her even though she dragged her son through the mud , cheated , stole from him and ruined his credit . This lady despises me for some reason. Her and the mother of his child are constantly attacking me . Idk what to do at this point .