Gf wants to be in a relationship but does not want to marry me

Firstly she tried me for a year, then I accepted her( have FB messages as proof). Then after accepting her behaviour changes. She had many male friends who doesn't belong to her colleges, coaching or relatives.. later got the info that she operates FB fake profiles to connect with stranger guys.. she use to be online most of the times, due to which we had verbal arguments.. after a year or so I got to know that she is having other bf too, with whom she was having physical too.. even when I contacted that guy he had no clue about me.. finally she cried a lot, then I accepted her gain.. we went to different places n even she use to stay in my flat during vacations.. when I told her to skip her bad activities, she told me to be in relationship just for physical sake.. I told her I am not interested in this.. but she blackmailed me by cutting her hand n threatening me that she won't leave me now.. in between she had other guys in her life too.. I told her to leave such things n marry me..