To betray you must first belong
It is quite senseless to keep reminding the betrayer of the success of their game plan by getting so shocked that they could take the least expected step and do so much harm. After all the whole sequence, including their efforts to belong pain had long been planned for the sole purpose to achieve the betrayal.
The only wise thing therefore, is to check it all from the first stage,the stage of belonging.You must set your own starndards of belonging and be sure to check that everyone who 'belongs' first fits the criteria for such belonging.Guess that's why people have learnt the difference between love and lust(just an example) and have known how to spare their hearts in the former and give their hearts in the latter. Its just one way to avert unnecessary disappointment.
So in the event of betrayal just take time to evaluate the first step, did the concerned actually belong and if they did was it rightful belonging?. In most cases the answer to the above is a plain no. So don't waste time mourning the offenders and asking them to reverse their actions, life is precious don't waste it. Just go on and mend your fences and learn how to control that crucial step, just who belongs and who doesn't.