What to do if wife has hidden her first marriage

Seeing my profile on matrimonial site and my wife approached me on facebook. She introduced herself as unmarried. About family she mentioned having mother, father, sister and brother. We became friends first, fell in love and later we got married in Feb 2015 without her family's permission. My family supported our marriage and we married as per Hindu ritual in presence on around 200 relative. I registered my marriage. Later, after inquiring about her cesarean mark on stomach I came to know that she was previously married and have son of 5-6 years from her first marriage. She left him because of his ill treatment from him. Her first marriage was not registered anywhere and she did not legally separated from her first husband. Bcoz of her lies i'm suffering from mental pressure which I can't bear anymore hence I want to legally separate from her but she threatening me of trapping under wrong allegations. She had also filed complaint against me of domestic violence and external affair.