legal consequence of blackmailing girls family to break her engagement

my name is Shubham Kumar. I am in relationship with a girl from 3 years. We both want to marry. But now the girls family is not approving the marriage. Her parents pressure has forced her to do engagement with another boy. Now the girl is also not in my side due to parents dignity. Even now whenever I ask her do you love me or want to marry me she always say yes but she also tell me that she can't go against her father will. Due to this I can't file any complaint or do anything. I tried to forget her but I can't. I can't live without her she talk with me secretly everyday. Now I am thinking of blackmailing her and her parents that I will give our photos to the boy and break the marriage if they will not agree to marry the girl to me. I know it's wrong but I have tried to convince the girl but she is not agreeing. If I do this can girl family file a case against me and what are the consequences or what should I do to be saved.