A False promise to marry

Dear Expert, My borther's girlfriend has filled a case against him for false promise to marriage under section 376, She was in relation with my brother for 4 year, in meanwhile they also made physical relation,as due to the intercast my borther initialy was not aggree for this relation, but she told i dont want any relation and i know i cant marry you, but after 2.5 year later she started to blackmail him for marriage,She started to abuse him, and threaten him to put him in danger, he some how made him understand about the situation and convinced her, but after some days she filled the case against him that is last year, my brother had all her SMS copy, in which she used to threaten him and blackmailing him, on the basis of that we got the bail from highcourt, now two days before her first ''Pesi ''was happend, in which she told i used to love him, but same time she has given statement saying he promised to marriage so i become ready to make physical relation, now he is denyng to get married. I griled about the girl and get to know about her, before my brother she also had one more boyfriend, and also got to know she had relation with some other boy, if my borther gets marrired her she will distroy his life, as she is not of good character, but it is difficult to prove it, please help me .