The OM is like a drug to her and the addiction will be hard to break, but if there is a will, there is a way and she will need to decide to end the affair. Then again the OM may end it if he gets tired of her.
Now, I do want to point out that it's not a good thing to play games w/the MLCer. They don't forget one thing that we say or do and they will remind you of it over and over again. This not the game called "Life". This is a real situation that is based on emotions and her decisions are all based on emotions. Snooping only gets you more frustrated about the situation and eventually, if you are not careful, you will tell on yourself. So nip that in the bud as well.
As for being a doormat...no, you don't play the doormat. You are a human being that has a lot to offer the world. Go out there and improve yourself any way that you can. Don't worry about what she's thinking of your right now. Why? Because she's looking through a pair of black glasses and can't see two feet in front of her. Don't tell her what you are doing to improve yourself...show her! Actions speak louder than words. Again, actions speak louder than words.
Stay the course, continue moving forward and live your life to the fullest for YOU!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.