I am glad that you had the difficult convo with W. I think for the first time she "listened" to your concerns and not blow them off like she always did in the past.
That is a new thing coming from W whereas in the past she would defiantly refuse to cease contacting the OM. I'd suggest that you let it be and monitor.
If W tells you that she did contact OM, you want to thank her for her honesty. Then state that it is no longer working for you and she has some decisions to make such as breaking off all contact with the OM. That would be also the time to insist that she compose a NC letter to the OM and have you approve it before she hits the "send" button.
All in all, I think it is a positive that she acknowledged that "it made you feel horrible and she'll stop."
Also suggest that you check out the Dear Peggy website for some tidbits on affairs and recovering from them. I think it goes hand-in-hand with DB really well.
