Ladies how do I get my ex back?

My gf left me 3yrs ago she was with someone after she left me. She is not with anyone now. Every so often we text or e-mail each other. We had lunch a couple of times the last couple of months. She left because of my neglected her without realizing it until after she was gone. I really loved her and at one point I know she was in love with me I realize how bad I messes up and what I did wrong. I am a different man for the better. So in your opinions let me know with your best answers in a situation like mine.