A guy is blackmailing and threatening me

Hi sir, I met this guy 4 years back when I was in college, through facebook. He claimed himself to be owner of an printing press and asked me to write articles for magazines. After an year as we came closer, I met him and realized that the pictures he had shown on his facebook account were not his own. But he begged for the friendship, and kept offering me help with many things and always forced me to accept his help. He got expensive things delivered to my home adddress and requested me to keep them. I could not oppose much because of the favors he has done and I did not want to be rude. Then he proposed me for marriage and I rejected it. Now he is blackmailing me and threatening me that he will spoil my life and will force me to kill myself. I have given everything back to him and even given him cash through cheque but still he is spreading rumors that have slept with him and I'' greedy for money. My parents too talked to him but he kept saying the same thing, either I should marry him or he won't let me live peacefully. I already know that I should have cut all the contacts with him long ago. But I was stupid and now I'm trapped. Please help.