HELP ME OUT

I am from South India. I was born in the so called Brahmin caste. I was taught that whatever your parents say or gives you is for the best and it is done with your future in mind. So there were a lot of not to do things added to my list. One of the main thing was never choose a man from another caste to marry. This is a sin. But i fell in love with a guy from a lower caste. He loves me for the person I am. He is there for me in all my ups and downs. On the other hand my parents do love me....But they hate my views and opinions. They want me to change. They want me to give up on him and marry the guy they choose or a guy who i can fall in love with provided he belongs to the same caste as mine. Everyday they are spying on me, sending me messages supporting their view. Its like i am in hell. I love this boy more than anything else. But I dont know how to make my parents change their hearts. My father threatens me that he will disown me if i marry this boy. But I'm determined in my decision because i dont believe in caste system. What should I do now? Please help me out sisters.