Peter, I was someone that was able to self-improve and I'm over 4 years with no regression. But I couldn't have done that without IC. I believe we can all improve and become better by putting in the work! But the key is not to do that for anyone else or to get someone else to change. The key is to do it for yourself! Because you WANT to be better and become the best version of yourself that you can be.
Also, to ultimatums rarely work and usually backfire on the LBS. Most LBSs want to save their marriage to the point that a WAS breaking or ignoring the ultimatum gets swept under the rug and just makes them look weak. Setting boundaries and sticking to them are way better.
"If this is done, I will do this action!" Much better to focus on what you can control (yourself) and not try to control what you cannot (the actions of others).
SteveLW and traveler are towing the DB company line. I call this cookie cutter advice which is not wrong. I personally give my opinions on a case by case basis based on certain situations and a feel for the LBS as a person. What they want you to do is detach/GAL/180 and if she cheats again you divorce her and move on. Your secret boundary was broken so time to move on and they sleep like a baby at night. What I am suggesting is you make it clear that if she goes sees OM she will no longer be married to you anymore. A boundary clearly stated and the consequences that come when broken. I would not recommend it if I didn’t think you would follow through. If you don’t follow through and she breaks it is game over. Now having said all that if she is hell bent on seeing OM then she’s going to do it regardless. If she’s on the fence a stated strong boundary may deter her from seeing him. So much of this stuff is about timing. Most peoples regrets on this board including myself is that they were weak little bitche$ during their situations. Don’t have those regrets later on down the line. If a PA is a dealbreaker then let her know it.