I got cheated from by boyfriend and now he is blackmailing me

Am in love with him since 6 years, he used to behave as good person , but recently when I went to write my exam of upsc I met him, after that I came to know that he laready married a girl illegally since 8 years but I lasted for only 3 days , and he had illegal affair with 2 other girls and he tried my sister too but she escaped, so my sister told me this incident after my parents agreed for our mrge, so now I am interesed in him , he cheated me, now I told him a lie that I got married and forget me, but he is not believing and blackmailing me about our kissing pics that he would show them to my dad, what I need to do sir please help me, and am an IAS aspirant I don't want to file any complaint which spoils my career.