Have a think about your boundary here. If she chooses to go and meet OM, what does that mean to you? Will you feel happy to share the MBR/bed with her? Will you feel happy to still live in the same house etc. Also, be sure that is what she is doing, and that you are not reading the worst into something else.
Once you are clear on your own bottom line here, you can let her know. Hey, it's up to you if you want to go and meet OM. But if you do, I'm not willing to X. It's your choice W.
And if she chooses to go ahead? Well, our choices carry consequences and the boundary will be enforced. Please don't approach this in a punitive way - it is not about punishing. It is about how you want your life to be (and not to be.) It is about your own wellbeing and the respect you have for yourself.
Good luck with whatever you decide.
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus