One month girlfriend blackmailing me

Namaste to everyone, I am a 24 old male from andrapradesh.I am searching in job for that preparing for bank exams.3 months back on June 19th 2015 a girl came to my home her name is sirisha to meet my mother to give her sweets sent by sirisha mother introduced her to me as she got bank clerk and I thought she can help me in studies and asked her to help.she said we can study together for bank po.then I regularly went her home for preparation her mother and father also is there in home.after few days she said "I love you" but am already in love with someone from 6 years.sirisha know that I told her in first meeting of us I.e on 19th June 2015.I refujed her proposal and we continued preparation by taking her promise not to rise this topic again. But as time goes I liked her and said I tooo love you in July 2015 our preparation going good but I felt in my heart am doing wrong because am already in relationship and realized she is flirting me and I attracted by her then July 23,2015 I strongly said her about our mistake and said this is wrong no more relationship only studies. After that she started blackmailed me that she will die if I don't listen her.but I strongly warned her no more relationship. Then on July 24 2015 she agreed that is her mistake to love someone who is already in relationship and said never raise this topic.from that day I started not going her home regularly to avoiding her at august 2015 I completely stopped to go her home.but she started coming our home then but in august 13,2015 I told her don't come my home.then she stopped come to my home.we did not have contact from then.on September 6,2015 I chatted with her in Facebook asking her a lot of times that"she will never disturb me" this question I asked her lot of times in that conversation and she also replaid me she will never distrubme lot of times.I have that masseges with me.but after one month on october 11,2015 she again started blackmail me to she will tell my parents then I told her I'll tell her parents about her then she said " I don't care and My parents will help me".then I went her home to tell her parents by the time reaching her home she said if I tell her parents she will tell about this situation to my girl friend parents".then I said I don't care after talking with her she again said she'll never distrubed me and she is promised on her mother after that I came to my home. NOW dear sirs what should I do my career is spoiling I am not able concentrate on my studies I don't trust her she may repeat this last out love relationship is only 10 to 15 days.I never sex with her only I kissed her and huged her that's it I never intercourse with her. Dear sir pleas read thoroughly my letter give me some advice I don't want bluff Anny one because of that I told her we are wrong and not prolonged my relationship. Dear sir I told about all this situation to my lover whom I have been in 6 years relationship because I don't want to bluff her she also for given me.