Just forget her, I had the same issue. My ex cheated on me, and all I could think about was her getting f*cked by some random guy. I couldn't even masturbate anymore. I kept picturing the girl in the video with the dude as my ex and this random guy. Then I figured, why the fuck should I even bother to think about it. There are a zillion girls who are alot better, nicer, and more faithful. Why would you lower your standards for someone like that. Keep in mind, that you are better. You don't believe me ? [youtube]
http://www.youtube.com/watch?v=ZVUyyHYkBHk[/youtube]