My take is a bit different and this is based on my experience only.
I pretty much feel once you file for divorce things are done. While it does happen, maybe more than *I* think, I tend to think once a divorce is filed that is it. So, if you are ready to file for divorce, ready for your marriage to end and ready to be 110% done then go ahead and file.
I understand the idea behind letting OW's H know about the affair. However, if you do expose it BEFORE you file for divorce you are giving both your H and OW plenty of time to cover their tracks, get their stories straight and create a scenario where the affair cannot be part of the D proceedings. If CA is a "no fault" state (I think it is?) maybe that won't matter so much. I would seek legal counsel before you do anything.
I rarely think divorce filings shocks a WAS into doing anything like many of us hope for... especially when there is a PA/EA affair happening.
