I know EXACTLY where you're coming from. It's tough being the bad guy or gal when it's really the other spouse that left the marriage. My wife literally started spending more time with the EA friend's family than she did with her own family but had audacity to tell me that I'm just jealous. Um yeah, I'm jealous for good reason...
See there, you got me going.
Anyway, my wonderful MC confirmed that it's an EA and has been very supportive. I owe her a debt I can't repay.