Mental harassment

I am Sanjit Kumar Verma, I am a friend of a girl who was in forced relationship of 2-3 years. She never had any feeling for him but he always blackmailed her that he will die he will do something and the reason will be you. She always tell the boy that she has no problem she will marry after he is accepted by her just avoid the situation. But now when she has taken step that she will not continue this forced relationship, she has involved the boy's family to make him understand, her family was also involved and requested the boy to leave her. But after so many efforts so many requests, the boy is trying to hack her social media, continuously going to the girl's college, coming at the gate of her building, calling her and her elder sister from numerous numbers to talk with him saying you have told me that you will marry me, you have wasted my 3-4 years, marry me, talk to me...this things and he forcefully wants to talk with her. Her innocent family don't know what to do. They always talk with the boy's family but having no changes. They told that they will go to police but in return the boy's brother also telling that he will also put a case against her. The family are afraid for going to police as they are not involved in police matters before and they also think the boy can be more dangerous for them after knowing about the case against him.