Girlfriend insulting me and threatening for suicide what to do

I had a realtionship with one girl since 2009. we are in serious relationship. suddenly last year her behaviours and attitude changed. she tried to put me in faults and also tried spoil my image in from of her family.later i realise somethning wrong.in last 7vyears many times i told her we get seprate but every time she cried and told i will b die, i cant live without u.etc etc. all this her messages in my cell till date.almost hundered of this thypes of sms while she begaging for relation and convnced me that she loved me lot . even she wrote 3 pages letter to me of same content. i still have thisletter. now she is insulting me while i try to talk with her.i rejected numbers of proposal of marriageonly for her as she told me wait for some year. in her letter she promised me that she will b with me in any condition. and even sms which i have.what can i do in it ?