I don't know you that well, and I probably will never get to know you. All I know is that you changed my friend's life, and it's not in the way you were supposed to change it.
1. You ruined her expectation of love.
As we grew up, we all had expectations of what love was supposed to be. We all dreamed that one day we would meet "the one," fall in love, and someday get married and have kids. Sure, you weren't the one that she was supposed to do these things with, but throwing around the word "love" while mistreating someone is wrong, and something that no one deserves.
2. You constantly tear her down.
It was bad enough seeing her in the fragile state she was in when you broke her heart, but having to constantly pick up the pieces every time you try and return to her life again gets tiring. It is hard enough convincing someone the first time around that it is not their fault, but doing that over and over again begins to lose meaning. I know you are not a bad person, and I know that sometimes you do mean well. Just remember that every time you decide to hurt her again, it gets worse.
3. You are both better than this.
It is important to remember that you are both worth something. I do not forgive you for the pain you caused, and all of the times I never thought she would be the same again. However, I know that you are capable of love and kindness. Go find where you are meant to be, and do something great, instead of staying here and creating a storm. You are both meant for great things, but not necessarily great things together.
4. Think of your future.
When you look at your future, do you see what you are doing now? Do you always want to cause destruction and beg for forgiveness time and time again? Think of your family, and think of the family you will have in the future. Think of the daughter you might have one day. Would you want someone to treat her in this way?
5. Love shouldn't be this way.
Love is supposed to build others up instead of tearing them down. Seeing what she went through was a hard thing to experience. For the sake of her, for the sake of her friends, and for her family, it is important to move on. While you do move on, try and remember what love should feel like. I promise it will be worth it once you realize it should not constitute pain and suffering.
As for my friend, she is fearless, strong, and one of the most influential women I know. She will get through this, and be stronger because of it.