Your wife is going all out to control the situation, and you, from as many angles as she can think of, without recognizing that many of her actions make her look guilty, and without doing the things that you need her to do, like open up emotionally, sever contact with 'Mark', and support you rather than fight you.
There are several actions that sound like someone preparing for a court case, rather than trying to repair damage to a relationship:
hired a PI for about $3,000
wants the PI to look at cell phone GPS records to show she and Mark weren't together for long periods
she now says she was trying to buy time so that she could later gather video footage, phone records, and witness statements to show that she was not with Mark on those dates or at those times and that the physical story was false.
Cell phone GPS records only work when people have their cell phones switched on. If one, or both, had their phones switched off, there will be no evidence, or incomplete evidence. If your wife knows enough to suggest using phone GPS evidence, she will know the effect of switching phones off. Video footage, phone records, and witness statements? Suitable for a courtroom, but all miss the big questions about why any of that is necessary, why she hired the guy, why he had to leave the school within a year, and why he came back and hung around so much. You aren't running a surveillance operation, you are trying to get at the nature and extent of your wife's relationship with the guy, which she keeps avoiding or minimizing. If she is the one gathering the evidence, she is the one who controls it, and she can leave out anything incriminating. Witness statements give her control of which witnesses to speak to, and which are best avoided.
wants Mark to cooperate
wants Mark to take a polygraph too
when she contacted the PI, she gave Mark’s information and told the PI that he was "willing to cooperate" and wanted this "cleared up too." She now says she was just assuming that and has not speaking to him, but to me that still shows she was treating him as part of her defense rather than someone she needed distance from.
You nailed it when you caught her out in her continued contact with someone she should have severed all ties with if she is remotely interested in saving the marriage. Instead, it sounds like they are working on a joint defense, which indicates more of a relationship than your wife wants to admit to. She just doesn't get it. It is almost like she wants to prove nothing was going on so she can continue her relationship with him, which is what caused this problem in the first place.
She is also insisting that I produce whatever evidence or "proof" I supposedly have, because she says she does not believe I really have any, and if I do, she believes it is inaccurate, misleading, manipulated, or even fake. So at this point, the situation feels less like a truth process and more like she is trying to disprove my conclusion.
A crude attempt at control, followed by the old 'fake news' ploy. Again, what your wife misses by a country mile, and what causes you distress, is that none of that is about proving her love/fidelity for you, repairing the damage to the relationship, or acknowledging the emotional pain this has caused you. Those should be her priorities, not exonerating herself in a court of law.
An acronym often mentioned in this forum is DARVO. "DARVO is an acronym for Deny, Attack, and Reverse Victim and Offender, a common manipulation strategy used by perpetrators (often abusers or narcissists) to avoid accountability when held responsible for their actions. By denying wrongdoing, attacking the accuser, and playing the victim, they reverse the roles to make the true victim seem guilty." There are elements in what you have been subjected to that fit the bill, and it is no wonder they have left you feeling distressed.
At the same time, she still sends love notes, wants affection, wants closeness, and says she wants to save the marriage while also telling me she wants to buy me out of the house rather than have us sell everything we own (rental properties plus primary residence).
Yet more attempts at control. Control of your emotions, and control of the potential outcome if a divorce happens. It all contributes to your emotional turmoil, rather than supporting and reassuring you, which really ought to be your wife's prime focus. I am sorry that you are being put through this. Many here have been through the same, and will support you. As far as any agreements or arrangements in the event of a divorce go, do not agree to anything before you have spoken to your lawyer. If it does come to divorce, you need the best outcome for you and the kids, not the best outcome for your wife (which she seems to already be planning for).
[This message edited by M1965 at 12:29 AM, Wednesday, March 25th]