Blackmail by student after intimate talk to avoid appearing exams

I m teacher in a pvt educational institute. My Boss Trapped Me By A Lady Student. She came to me intimate and forced me to tell sexual talk with me. Now she and my boss trapped me and they planned to inform the institute head about that and he is their side. One of boss is my side. I have sms her via Facebook where I wrote to meet one day as she told me same in same sms. I wrote some intimate message via whatsapp but do not wrote any sexual talk to her. Each time I want to make distance with her but she came closer. Only 4-5 times she intentionally created the situation so I told her some sexual talk to her and I trapped by her by told this f2f but not via any written sms. She had no contact with me for last 4 month Now plz help me what should I do. The all thing happen in February 2017, she passeed the course in June 2017 but she retain upto June 2017 ( I think she have the intension to trap me so she did not appear in one exam in final year). Plz help and told me why at to do sir?