How do I win my girlfriend back after cheating on her with three people including her best frenemy?

I've been dating this girl for almost a year and I cheated on her in the beginning, middle and end of our relationship. The last time was with her best friend who has been holding a grudge against her for a long time. Her best friend was the one who told her what happened and then I confessed to the other two times myself. She has never cheated on me and loved me despite my problems. I'm trying to win her back, but I just can't think of anything fitting. She feels like what she thought was her's and completely untouchable by anyone else(my body) is no longer her's despite my insisting that I will love her forever and always. I was thinking of fixing that issue by tattooing her name on my chest in the possessive form ('s) in order to show her that I am truly hers forever and always. Other than that, I can't come up with anything else. Any suggestions?