First off, don't ever underestimate an EA. My W has been having one for about 18 months now and is about to leave to date the OM. It is just as devastating, and more destructive than if your wife went out and had a one night stand. I used to think its 'only' an EA and how lucky I am that it wasn't a PA. Boy was I wrong - there is no luck in either case. OM has taken your place as her opposite-sex companion/friend, etc.
How good is your proof? If it isn't great, such that she can just say 'we are just friends' you might hold off. However, if you have phone records or recordings that she would know would be interpreted as inappropriate 'friendship' then you might want to lay it on the line.
The risk you take is that she goes nuts and decides not to go to Retro, but the fact that your W is in the state she is in tells me that the EA is a serious threat and is probably driving a lot of her behavior.
I discovered the full extent of the EA during retro, and was like you beforehand with a strong idea that one was going on (mild proof at the time as well, such as her change of behavior and how she was hiding her phone). I wish I had known all up front and confronted her BEFORE retro started, because OM knew we were going and stepped up his contact while we were in the program.
ME/XW:47 S21, D19, S15, S14 M:21 T:26 W moved 6/10 I filed 7/10 D final 4/12 remarried 8/12 W wants to R 12/10 and 4/11 but I decline
