This soap opera will continue until you put your foot down and make it very clear to her that she is playing a very dangerous game that will end in destroying the marriage. If you don't think that her meeting in a hotel room is not going to end up with him boinking her you are dreaming. Of course, your wife knows that. Otherwise she wouldn't even consider meeting him there.
As I mentioned in my other posts her words to you about wanting to rebuild the marriage is not backed up by her actions. Furthermore, I would not be so sure that she has not had sexual encounters with him already. What this calls for is giving her a strong reality check. I would have your lawyer prepare a letter stating that you are not prepared to stay married to her since her intention is to commit adultery which will result in a divorce anyways. Since you are not prepared to stand by and allow this to happen you have given your lawyer instructions to begin the process to divorce her. If on the other hand, she chooses to stay married she will end her relationship with this OM immediately and show that she is committed to doing whatever is necessary to earn back your respect and trust.