Fraud on the name of marriage

I am in a relationship since last 3 years. The boy was ready to marry me since starting n his parents were ready too. He used to take me to his home n let me talk and meet with his relatives all the times We are living in same building just different flats. He stays with me as well, like 1 day or upto 1 month. We are in physical relationship as well. From starting my parents doesn't know anything. Now in Jan 2015 her sister died and after that he and his family are looking for another girl for him. We are from different casts. But still he keeps saying that we can marry if both the families are ready. He is convincing his family since july. And he asked me to wait till he talk with them. Now suddenly 15 days back his parents set him with some other girl by emotionally blackmail to him. Then he tried to convince me to forgot and move on. But I wasn't agree to do so. So he asked me to tell my family. My family is ready but now his family is giving excuses of cast n all. I want to legally sue him and his family. As they were keep promising me about marriage. And I am feeling harassed and being part of fraud. Please help to know my rights. It very urgent. Please reply asap