Well first off...don't plead with her. Pleading will appear needy, needy is a turnoff...avoid that.
Simply flat-out tell her. "I'm sorry for what I've put you through, I really do understand now how badly I've hurt you. I know you have no reason to believe me at this point so would like to ask you for the opportunity to show you through actions. I know you feel you've already given me too many chances and have wasted too much time waiting for things to get better but I would like to ask you for six months. Six months to show you through actions that I am seriously addressing this issue and am working to make permanent changes and SHOW you how much you DO mean to me. If you feel you cannot give me that time, I will understand...but I also ask that you not shut the door on us. Can you give me six months? It's not that long in the scheme of things."
Something along those lines. Don't grovel, don't beg...just state your case and your sincerity. If she says right then that she doesn't know...don't press. Just tell her you understand she needs to think about it and let her know you will get back with her in a couple of days to give her time to think.
