Keep it short and to the point. If she knows nothing about this it will clearly upset her, especially the parts where her husband declared love for your wife.
I believe that you have told your wife of your intentions to tell his wife, if so she may have warned him and he may have told her anyway.
I did say to W that I was going to inform OMs W but haven't mentioned it since and allot of water has passed under the bridge since then so I don't think it's even on her radar, plus I said I'd need her help as I don't where to start looking. Once I realised that I screwed up telling her that I taken it under ground which is what I should've done in the first place.
Secondly W is extremely unlikely to have contacted OM about this or anything else. A month ago she wrote him an email that I was apart of to OM outlining how much their correspondence had hurt me and jeopardized our M and she would never be in touch again and asked him to respect hers/ours wishes.
I am checking daily for any sign of comms and as expected nothing to date so highly improbable.
I did screw up though, I sent OM an email the day after Ws email outlining what I thought of him a married man constantly declaring undying love for my W and how would he think his family would feel reading the email trail. I did however say this as a question as opposed to a threat. The worst case here is he's gone and covered his tracks (deleted all emails from W) which wouldn't be great but not terminal as I still have the last 2 years worth safely storage in cloud. I certainly doubt he would've confess to his wife based on my email as it was non threatening just my feelings.
On a different note while researching OMW I did discover that OM and OMW were married early in 2013 (just a few weeks before we moved countries and close to time they meet for lunch) and as they have 2 adult children and W said he was already married but it wasn't a happy marriage I'm guessing this was a vow renewal, I guess that proves he was either feeding my W lies about the state of his marriage or he's a complete ****wit renewing his vows all the while actively declaring his love for my W at every opportunity. I've got a photo of OM and OMW on the day (from facebook) they renewed their vows smiling away, I'm going to swipe that smile of his smug face
I was originally going to show my W the photo to show her the human face of the other victim a real human, but I've pulled my head in as that would alert her to the fact that I'm actually going to contact OMW. (See I'm learning!!!)