Its not can a girl do it? Well I have seen many guys cheating like that as well..Its the human nature I guess. People go crazy!May be she lost interest on you thats why she did that to you...But you have to understand that LIFE GOES ON..SCREWING YOUR LIFE is not gonna prove anything .. It will rather show her that you are WEAK. Even though when comes back to you..you won't be happy... Get Over it.Too many fish in the sea..