I cheated on my girlfriend?

How should I tell her that I sent other girl a pic of me naked, I know what the ****. I know I failed her, she gave me so much and the first thing I did was send a pic of my penis to other girl when I got too horny, I am every insult you can think of, scum, trash, piece of ****. The next morning I saw her and I looked at her with guilt, she returned the look with absolute love, I tried telling her, I said I didn't deserve her and she asked why and all that I could say was, "because i'm mexican". I should be honored that such a beautiful white girl laid eyes on me, I pictured a future with her but now it's over.