Forget about her and move on. Don't take her calls, especially when she calls a month or two from now saying how big a mistake it was. Don't, simply move on. Girls are cruel, deal with it. You now know the simple truth of female hypergamy. They are always trying to find someone better and only realise their 'mistake' after they have committed the act. Either deal with the fact of life that you will be cheated on countless times or try to find a woman who actually controls her fleeting emotions and stick it out with her.
And never, ever allow a woman control of your heart. Always be prepared to drop her at a moments notice, without a second thought. If you do that, you won't feel nearly has bad next time a girl cheats on you.