Stop contacting her. Go out and live your life. Become a better person for yourself. And she will probably come running back to you, but more likely than not you wont want her back at that point.
If you decide to beg, plea, tell her you changed, I know I messed up, but I love you, I need you and so on you will just push her away forever.
Anyway if she is really important to you I would stop contacting her all together buy this book and read it.
Love Must Be Tough and follow the advice within.