Not Over, you are in a perilous position, but have fared much better than most. Good job on your self-restraint and DB'ing.
Your W is in a very serious EA (at least), and is drawing an intense amount of pleasure from the excitement, validation, and attention. You cannot compete with that. It has nothing to do with you versus OM, it's "an affair" versus "a long term relationship" and the second cannot compete with the first, even if he's Marty Feldman and you are George Clooney, the affair is simply more exciting, so viewing it as a competition you will only torture yourself.
So what to do?
I can guarantee you that if you confront her, you will make things worse between you. She will be angry, and any and all resentments toward you will be exacerbated.
If it does come to light or come up between you for any reason, your goal is to not increase her resentment. Your best bet is to normalize without condoning: "Everyone likes attention from the opposite sex, I'm sure you felt lonely and somewhat hopeless about our relationship." Any scolding, application of guilt, or displays of sadness will make her resent you more and drive you apart. It's a tough place to be.
Since she is still talking to you and has ML with you, she's clearly conflicted and may be cake eating, thinking she can keep both relationships going.
I would *strongly* encourage you to talk to a DB coach on this site since your situation is in such a fragile state right now, you will win this one on nuance. They are very good and they can help you.
Here's my near term advice:
1) Stop snooping, you now know what's going on. Continuing to watch the pot boil will only hurt you. It becomes addictive, and your imagination will make things much worse than they really are. Let that go, she's having an affair, you now know it.
2) Continue to give her space. This isn't going to be resolved by jousting OM for her favor. As long as he's involved, you pretty much have to acknowledge that she's going to do what she's going to do and you really can't control it. You should also set your own expectations that this isn't going to turn around quickly, you're looking at months and months, not weeks.
3) Decide what you want going forward.
4) Continue to be friendly and supportive, but at the same time GAL, Act as If, and continue with your 180's.
Read DR if you haven't.
Acc
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015