I f**ked a girl over...how can i regain her trust.?

I f**ked up a friendship with this girl i have serious feelings for and she knows it. I started talking to her ex after she told me she didn't care, but now she has lost all trust and me and says that she doesn't give people second chances. I know there is way somehow that i can regain her trust, and we can be friends again. Do you have any suggestions as to what i can do to regain her as friend and regain her trust? Please help, i can't stand losing her, i have been miserably depressed ever since she has been ignoring me. Oh and i have already stopped talking to the dude, and i have already apologized a million times.