because as a child who suffered through it, cried about it and knew damn well the pain the kids and the BS went through. She should have thought twice about being a cheat herself. But of course in her eyes her situation was special and different. So she gave herself a pass
Come to think of it, my MIL's father deserted my MIL's mother & her when my MIL was 3 yo---I don't know why. My MIL destroyed WH's family when he was 3 yo., repeating the nightmare.
However, WH claims that he didn't know why his parents divorced until after Dday (altho everyone else knew, & told me). He really had his head buried in the sand. His mother had him so brainwashed that he never asked questions. He has always been terrified of her because she was so full of rage. (Even now that he knows this new information, I don't know if he will confront her.)
One of the bonds that I thought WH & I had was that it was so important to both of us that our kids have the secure foundation of an intact family that neither of us had (in my case, not because of infidelity---my parents were too religious, but because my Mom had cancer for years during my childhood & then died when I was a teenager.)
I guess when WH started up with OW , the unicorns & rainbow factor made him forget just how important this is, so the nightmare repeated for the 3rd generation in a row.