My daughter threatens us to commit suicide

Dear , my daughter had an love affair( not sexually ) with 3 persons in 2 consecutive years.. at present she is 18+ and the guy she has a relation with is 21+ . Now we are fearing that these guys can take advantage of my daughter( sexually).. And if that happens we will have no face in our society ,and we can never get a good partner for her.. At present she is so desparate,that she does not even care our guardianship when she goes to meet him.. we can not prevent her from meeting with him or contacting with him. We have proposed her to get married with the guy she has relationship, or to get married by our choice, but we don't want to leave her unmarried. She refused to marry that very guy at present, she refused to marry any other person either..she is threatening of committing suicide if we try to get her married. Her counterpart also refused to marry at present. If I let my daughter to do as she wants, she will obviously make us malign in our society that we think. ( Hindu )