It is not about how good a liar our WAS is. Mostly they are probably very bad liars. It is really all about US not wanting to believe the worst. So we choose to believe things we know are blatant lies. That is until we wake up.
As a result, as you try to put your M back together, trust is going to be a MAJOR issue (in my sitch too and I might post more on this later.) I find that as much as I want to believe what my H tells me, I've been lied to so many times.
Sorry for the reality check. Perhaps it was only an EA, but for the long-term health and happiness of your M, you're going to need to accept that it most likely was a PA and move on. I know it sucks but once you pass the hump of acceptance it gets easier.