My girlfriend is blackmailing me

We met three years back in college. Everything was fine between us initially. The problem started two years back, when my grade was better than her in college. She started abusing me in front of everyone, she abused my parents. She even went on saying that I sleep with other girls for money.Somehow, I consoled her cause I loved her. Now, I got a job, and I had to stay away from her.She started again, everyday , this time the reason is why did I like a profile pic on facebook, why did I go for a movie etc etc. She started saying the same words, calling my friends over here (who happen to be the mutual friends) and maligning my image , abusing my parents everything. She even started blackmailing me saying that she would commit suicide and make me responsible for her death, She started saying that she would tell everyone that I had sex with her if I don't marry her immediately. The truth is we never had intercourse, just kissing and touching happend between us. I can not concentrate on my work,my personal life has become a hell. Please provide me some suggestions. note: I promised her to marry, but I never had intercourse with her.