Don't want to get married

Hello, I am Mayank age 32, occupation business, I met a girl Priyanka 3 years ago, she from SC caste, we had a good run with some ups and down, she involved me with her social groups and with her family I felt comfortable, even went out to himachal for a vacation, made physical relationship and I told my family as well about her, both of our parents met but my family doesn't want me to get married to her due to cast. Anyways that's the background, now the real reason for not to get married is now I am feeling scared of her anger, I feel very scared to take a responsibility of another as she is not doing anything and I am very sure she cannot do anything in future as well, she'll be dependent on me in future and I cannot take her responsibility, if my parents throw us out, she is threatening me to be in a relationship since everyone knows about us and its an obligation to get married. She is talking like pschyo these days, her this avatar I have never seen, she threatening me to kill herself and all kind of things which is making me very scared. I am not seeing my future with her. What will I do, do I have to marry her or can we go somewhere where all our family sit together in front of any legal representative and sort these things out without making a mess. How can I go all this away quietly and maturily