Pleaser can someone advise how I now deal with this? I cannot force NC, I cannot get W to realise that this is an EA and the damage it has caused.
She says he understands her, they have a lot in common etc etc
First, I doubt she would have told you about him if it was physical.
You are correct that you can't force her to do anything. But you can control your response to the EA, and this includes even laying down an ultimatum should you choose to do so. Now I'm not recommending you do this, I'm just pointing out you do have choices here.
Giving her the article probably won't help.
Do you guys talk much? Personally, I would try to figure out why she confides in him regarding your M more than(?) you. Why does she think he understands her better. She brought this issue up to you so there is some comfort level between you. Maybe try to build on this, as a way to work out your issues. Allow her to keep telling you about him and what they talk about.
When she stops talking about him you know it went physical. Keep us posted.
M: A really long time. Crisis: 5 years. She's still worth it.
Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl