You have a very skewed sense of what you can control here. You aren't "allowing" her to go to him.
I think your achilles heal here is thinking you have that much control. The pressure is torturing her but it is from within her...she puts it on you because of course you left her and got this ball rolling. But now, fair or unfair, her feelings and behaviors are HER responsibility. And the worst feeling in being the LBS is that you have no control. So if you stop carrying that bag for her, and let her handle her own life, I think she will be better off.
You must let her know that her choices are hers to make and you can only control your reaction to them. You are in a triangle and I think you need to get yourself out of it.
She has pulled the kids out of the equation which is awesome so I think in some way you can exhibit support for that choice (subtly). And now SHE has to figure out what to do about OM.
There is a lot of mind-reading here too. She tells you x and y but you don't REALLY know where she's at.
Maybe the best thing you could do is remind her that this weekend isn't the be all and end all and that whatever she decides, she should remember that everyone will be ok and there will be new fish to fry as there always is...
