Is the progression common - EA, then EA & PA and then just EA?
No, it's not. Not more than just temporarily, anyway (often an illicit couple will agree that "We need to cool it for awhile; my spouse is really watching me," or whatever, but the physical affair soon re-ignites).
I don't mean to be harsh, but men don't usually (ever??) stick around for more than a year without physical pay-off. I would HIGHLY doubt, if this woman is local (and a co-worker), that their affair is not physical at this point.
You mentioned you are still ML. Please be careful, and use protection!
