Saying maybe not bc I have blah blah to do. I let her talk with the lame excuses then finally say come one whats the deal. Her reply, "Well OM was supposed to go somewhere and hes no longer going so now hes going to find out we went somewhere together". I went silent for a second. Should I explode or agree is what I was thinking. I finally said look, I'm not on OMs timeclock, if you got something important to talk about you know where to find me. This situation is just not working. She cried then said Ill file divorce paperwork. I calmly said that's your descision.
I think the first thing you nailed. But I wish instead of "thats your decision", you take some power over the situation. In my opinion, you can state at that time that you arent interested in being in any kind of relationship with her while she is seeing OM. And end it there. Saying 'thats your decision' makes it come across like you are comfortable being her plan B if she decides not to file...like youre always going to be there waiting for her to pick you.