My ex cheated on me, help?

My girlfriend dumped me around a month ago, with no real reason, which although was hard to take I respected her decision. After this I ended up hooking up with girls she probably wouldn't have approved of and when she heard she gave out to me, alot, and made me feel awful. Yesterday I heard she cheated on me, having sex with a guy she hardly knew, and all though our relastionship she was anti sex before marriage which I always respected.When I asked her about it she told me, but then tried to turn it on me with feeble facts. I know its petty but I don't care and I want my revenge, she treated me horrible and hypocritically gave out to me for hurting her after she was lying to me and hurt me alot more. I can't just let this go, I know its in the past, but I don't appreciate people treating me like ****. What can I do to hurt her?