stuck - you said: "She still works with the OM although not directly with him. So she sees him several times a week. I do trust it when she says she keeps everything professional with him."
I hate to tell you this, but because she still works with him, she is still having an affair with him in her heart, if not more than that. She simply cannot break free and get over him if she is seeing him at work. She must change jobs (or he must) and if she does not, its like a crack addict who is trying to get clean, but who gets just a tiny taste of it every few days, and therefore never gets it out of his/her system enough to be fully clean. And when this type of thing happens, because there is still a little bit in their system all the time, they are very vulnerable to just jumping right back into a full on addiction (or affair) at any moment. Its "right there under their nose" so to speak. To resist requires incredible strength that an addict generally doesn't have.
This is probably why you get the feeling she could run at any moment.
Stuck...I know that you feel she will not stand for any ultimatums from you, but if you want her to ever be able to break free from her feelings for OM, she has to leave that job and go NC for ever. There is no other way.
Whatever you have to do, even if it makes a really uncomfortable situation for a while, it will cause you less pain in the long run that what you will feel when she starts up an affair with him yet again.
