You can’t control her you can only control you. You have options. Here are three: (1) ignore the behavior/wait it out and hope it stops, (2) confront her and constantly call her out on it which may drive her to move out and in with OM and/or file for d, or (3) you can decide you will not be in a relationship with a woman who is in a relationship with another man and file for d.
Gordie 40s W 40s M20+ kids 2016 BD W fantasy affair w OM1 I do everything wrong 2017 I start to DB W says TLTL files for D PA w OM2 2018 I do LRT W drops filing and OM2 situation slowly improving