Our therapist explains it as Dissociation.
According to my google search, 'dissociation' is a catch-all for personality disorders that can't be explained/categorized?
IMO it's a convenient way to avoid the therapist judging a your wife by their behavior and/or holding the person accountable for their behavior.
Both her therapist and religious beliefs provide her with a get-out-of-jail pass with respect to consequences for inappropriate behavior (including the card 5 years ago).
And although I understand why you offered her a second chance 25 years ago (we've all been there), you also offered her another get-out-of-jail pass.
A pass that she forfeited with the birthday card 5 years ago. Plus, is my recall correct, at that time you also discovered in her office that she saved a souvenir framed photo of her and the OM?
At a minimum she should have been exposed to your friends, family, and church members. Why? because it's one of the few consequences for adultery - and because they trusted her, they have a right to know 'who' your wife really is.
I suggest you consider:
1 - finding another therapist. Why? because he's not helping you. At best he's simply providing a sympathetic place for your wife to unload and feel good about herself.
2 - I'm not sure therapy for her will help at this late date. She seems to have won (she gave herself a multi year romance and got away with it).
Finally, I can't explain away the birthday card (just like your therapist can't - or won't).
IMO, the card (and photo) is hard evidence that you were plan B, that your wife still has positive feelings for the OM; lacks empathy for you; and guilt & shame are not a constraint on her behavior because she knows she will get a free pass.
Neither your wife or your marriage was or is perfect. In addition to carrying the pain of betrayal you're also carrying the burden of smiling and living a lie to your family.
If you decide to run out the clock (live with her) consider exposing the enormous burden you are carrying as well as the enormous sacrifice you made 25 years ago to hold your family together.
Specifically, expose her to your kids (without warning her). And inform her that your pain is 1,000 times greater than her discomfort.
And when she asks why you didn't warn her: reply it's dissociation.
[This message edited by Robert22205https at 10:19 AM, July 11th (Saturday)]