Consensus Relation

One girl proposed me and fro the begining I told I can not be in love and if marriage happens it will be arranged by our 2 families and if horoscope matches then only I can marry. But I cant be in love relationship. I never promised her to marriage instead I have sent messages for my unwillingness to marry her and she agreed to that and told she will not go against my decision and wants to meet as a friend only despite my objection. She is a family frined so I could be harsh on her. We were in physical relation though there was no intercourse. She forced me to but I told as I can not marry so I am not going to do that. She used to send me lots of bad picture and used to provoked me to chat dirty with her. I used to chat dirty over her pics and she used to reciprocate. Now she is blackmailing over all those chat message and thretneing to sue me if I do not marry her. She sent all those message to my family members and turnisnhed my image. What can I do? Even after knowing that I cant marry her if she comes to me and send me pics does it make me guilty?