Love affair but engagement with other

Sir, actually my girlfriend loves me alot and I also. But, girl's family doesn't understand. She is from Yadav community and the family wants her to marry in the same caste. She is 25 and I'm 28. She has been engaged 4 months ago. But, she didn't want to marry him. The boy whom she's going to marry came to know about us and from last 1 month, he is constantly torturing her mentally physically both. He had installed camera recorder, voice recorder in her phone and still, he's constantly monitoring her and everytime he talks with her, he tortures her. He has 5 to 6 times physical relationship or sex with girl forcefully as he'll be her future husband. He also frightens her by saying that he doesn't want to marry her She's living nearby his office in a pg but still in morning, evening, on phone, everytime, he fights with her. She's depressed and lost around 10 kgs in a month. Her family is narrow minded and is not supporting her. Her family live in a village and they want to save their dignity, izzat whatever and they don't care about girl. And, since her father passed away 2 months ago, she doesn't want to trouble family anymore. She's not happy, depressed, constantly troubled but doesn't want to say anything. What to do sir? Please help.