advice on boyfriend haressment and blackmail. how can i legally deal ?

Hi, me and my bf have meet by social media. we r in a long distance relationship. he is from south india and I am from north india, things was good but slowly he started becoming angry on little things, and if i use any social site he use to get angry and started to abuse me, i cannot speak with a singal male person not even with my family member.he does not let me go out from home i cant wear the things i like and i thought after meeting his insecrities would end and meet, but after he went back he started blackmailing me with our photos, he took my mail, my all social site acc, when we met he told he would marry me and even went to temple and gave me mangalsutra,but now things have even gone worst, when he gets angry on anything he tells me cut ur hand and show me the blood, if i didnt do then he will blackmail me telling that he will send our pics to my family and every1 on social media. I am bound to hurt my self even if i dont want. I dont know what to do. Plz suggest.