Ya know, the WAS having the affair is behaving no better or worse than the OP, with the exception that the WAS is the one CHEATING on you. Obsessing and brewing about the OP is really not useful. If you think the OP is irretrievably evil/damaged/selfish/disfunctional/whatever, it is unclear why you would not feel the same way about the WAS.
Focus on yourself, not on some third party who is a symptom of the problems in your M.
