When we remove that 2nd choice, fear, jealousy & fear of loss motivates the WAS to make a choice or if we look at this from the LBS perspective, we remove the choice that the WAS had, we remove ourselves from the options list and we show them that it's our choice to make and if we do this by dating, don't we communicate indirectly that they no longer have higher value.
Dating as an act of revenge (creating jealousy, fear) or as a means of moving forward with your life? It would seem to me to go outside your marriage for emtional and/or physical companionship in these cicumstances, conveys, not necessarily directly to your spouse but to yourself, that you have thrown in the towel. And yes, they no longer have higher value, very little value in fact since you now have a "new toy" yourself to play with after realizing the "old toy" and your need for them is really just a train wreck you are trying to salvage parts from.
I think also, that, many of these WAS spouses are in self-righteous mode. And no matter what they do is correct in their eyes, but what you do, if you are mimicing their behavior can be another nail in the coffin, so to say. Fine line to thread here.
Is it a decision we must make between personal happiness and what works to maintain a marriage? Steve.