My mouth is too big. I had to tell EVERYONE. Confronting OW didn't do a thing (except make her angry and give my husband an earful of her anger), but telling her H made her absolutely frantic. It added difficulty to her marriage and forced everyone to deal with the reality of the situation. Apparently, OW wanted to stay in her marriage because she immdiately cut off the relationship with my H.
Perhaps it would have pushed my H and OW closer together, but I was too angry to care and I was too intent on doing whatever I could to make her life (and their affair) more difficult regardless of where it went. Although my husband was already intent on divorcing me so it didn't matter. But even if he hadn't been. I probably still would have done it. And that's just me. It's a personal decision.
(P.s. No one knows Mark's sitch but himself. No one else is living it, and knows the people involved and all the details about it. And no one but him knows better, what may or may not have made a difference).
There is no arriving, ever. It is all a continual becoming.