Recovering from infidelity is a very long process, irrespective of if you divorce or reconcile.
I can share that I ended my relationship and thought I was "over it" about 2 years later, only to have the good sense to seek therapy about 15 years later to finally deal with the PTSD infidelity gifted me. In retrospect I don’t think I was capable of dealing with the PTSD for maybe the first 2-5 years, but had I recognized it earlier I could have been rid of it within 10 years. Some things simply need time to mature, slow down, become recognizable.
Not saying you should wait 10 years, nor that you will take 10 years. But rather making two points: This takes time, and there is recovery you need to make irrespective of if you remain married or not.
As a young cop the veteran who trained me made an astute comment: He told me to notice than no matter what, the very vast majority of people would excuse or mitigate anything wrong they did. Like nearly everybody I stopped speeding would comment about just following the flow of traffic, I should focus on "real" crime, they had an emergency or whatever. Wife abusers would explain – in detail – why they had no option but to beat her senseless. Burglars would whine about how everyone is insured and would get a new TV paid by the insurance – basically doing them a favor. Heck… the worst I ever heard was the guy trying to convince me that 10 year old boys enjoyed getting oral from him, therefore no harm…
We do this too. I’m not losing weight because of my slow metabolism (something I can’t control) and it hasn’t got anything to do with the cake I allowed myself…
Your wife was capable of initiating, entering, and being in an affair. At each and every minute of time for all those years she KNEW it was wrong; knew it was damaging. I get it that she compartmentalized, that she never thought you would know and that she thought she would be able to keep this a secret all the time.
I get it also that when any semi-sane, normal person looks at all this they are thinking "WTF! How could she imagine all that?!"
Maybe your first evaluation might be if the above is "normal" thinking for your wife. Can she compartmentalize other things in life, does she show rich narcissist behavior, has she shown a two-sided moral compass on other things in general? Like… is she nice to kids but kicks kittens?
This is why – if this was an ongoing affair – I would be telling you as loudly as I could to expose it to all stakeholders. Like… We can imagine that back then when the affair was ongoing she would be thinking "Alas! In a fair world I would ride away into the sunset with my soulmate Mr WonderSex and live on lobster and steak for eternity, but the Evil Ogre my husband has me trapped with 3 kids, a mortgage and a planned holiday to Disney"
Once exposed – once you tell her she’s free to be with Mr WonderSex her soulmate and there is nothing holding her back… these compartments crumble fast. Fantasy becomes reality. Even if soulmate had left his wife for her then she realizes he too drinks beer while watching the Sunday game, farts and scratches his scrotum. Nobody is happy for her. Nobody thinks she’s justified in the affair…
But you aren’t dealing with an "active" affair. You are dealing with a wayward spouse that has been battling the justification of her affair for years internally, and now in some desperate attempt to save her marriage/status/lifestyle/reputation….
Frankly – to expect a "real" why from her now is not realistic, because she’s not clear on the why herself… It might take months of therapy.
I suggested you give yourself a timeline – a deadline if you like.
Set yourself a goal for what YOU want, and what you can realistically get. Like… I personally think that within 30 days you have the "truth" on factual info. Things like when started, how carried through, when ended, ongoing contact, who knew, where, how…
Maybe even make it clear to her that her truths will be validated with a polygraph. Explain that it’s a tool for her benefit. If she passes it indicates honesty.
When that day comes – say the 20th of April – you can evaluate if you have a believable picture of the factual reality. You can evaluate with yourself it what you have is enough for you to decide there is no hope. You can then set yourself a new target and a new date. Like if on the 20th you believe you have the truth, then set the 1st of May as the deadline for a polygraph IF you want to remain married, or for the date where you have hired the attorney.
This is a marathon. The goal isn’t 46.145 yards wide and 2 yards ahead of you. The goal is 46.145 yards AHEAD of you, and your path towards it narrow. The pace and who you run with is up to you.