surviving infidelity

As with many people who are suddenly left behind by their mates because of a side dish, I have been on the end where said mate suddenly comes back, claiming to have had a change of heart and a desire to make our relationship work again. In the past, I have always been confused on whether or not I should give the cheating shmuck another chance, and have chosen one or the other option at one time or another. Some ended in good ways, others for the worse. Given the chance, I would have welcomed a source of advice on how to handle that kind of minefield situation.