I'm so sorry that you are dealing with so much pain.
Your WH treated you and your children horribly.
How can people do this? Just discard their family for a total stranger?
It is such classic mid life crisis.... he is running away from all of his responsibilities.
The affair is his escape. It is such incredible selfishness.
But,unfortunately, there's nothing can do. You did nothing wrong. You were being the best wife and mother that you could be.
At this point you need to take care of yourself, your children, your grandchildren. It sounds as if your kids have rallied around you.That is a blessing.
Have you gone to IC? That was so important for me. And I did need to see a doctor to get meds for anxiety and depression after d-day.
A betrayal like this is traumatic and many of us suffer from PTSD like symptoms.
I know I did and I ultimately reconciled with my FWH.
Your situation is heartbreaking.
A book that was helpful for me was: Transcending Post Infidelity Stress Disorder by Dr. Ortman.
He gives good advice on how to accept and move forward after experiencing the trauma of infidelity. The advice is good for those that try to reconcile or decide to divorce. Either way Dr. Ortman believes that the BS needs to come to terms with the trauma of the betrayal.