My DD was delighted when I got divorced.
I would be delighted if my father divorced my mother, she bullies him totally and behaves like a tantrumming child.
My friends father is in the same boat and she is so sad about it.
Another friend of mine, a bit older, says of sex "oh, I cant be bothered, I presume he sorts himself out" and harps on about her bloody conservatory.
This is a completely grown up "family" (DCs) with their own lives. Not 3 toddlers/school aged DCs.They will always be "family".
I have a feeling the OW has been in a full on relationship for at least 4 years with the husband and it is clearly much more than sex.
OP is emotionally immature and hugely lacking in life or relationship experience outside DCs, years ago, and her bubble. A PP comments that the posters were younger and do not understand a 40 year marriage, is telling; I am in my 50s and have far, far more independant life experience. I imagine most would. Just a look at the things some women have to go through on other boards shows you that. Life is for working at; you do not threaten suicide.
People do have to take responsibilty for marriage breakdowns and they have to deal with really heartbreaking situations (involving sickness, DCs, tragedy) They have to ask themselves difficult questions, grow, adapt. Much has changed in attitudes in 40 years.
He should not have been unfaithful but he was and is, clearly unhappy.
Of course, I could be totally wrong... not 4 years, emotionally and work connected relationship and strong friendship and simply a menopausal piece of incompetant and desperate "fluff" entirely to blame, with her wiley middle aged ways.
OP refuses to answer the question of the relationship 4 years ago though.
I do wish you well OP, but while you are in denial, nothing will truly change.