Wow, bro..that was cowardly doing it in an email. You did the right thing by not saying anything derogatory to her or expressing yourself. Anything bad you say now during the pain and anger will only be brought up again if you guys get back together. The last time a chick did that to me she was getting ready to bang another guy. Chicks feel guilty if they cheat on you so they will break up with you so they don't have to feel guilty.....about anything. I'm not saying she is doing this to you, but it seems like it's a part of the female mentality. Don't do anything you would regret when she gets back just in case you plan on getting back with her......unless you don't want to get back with her. Then the best thing is to nail some other chicks..that always made me feel good again!! Good luck bro.