For many people these are sadly lifelong hurts.
Someone I know had met the love of their life, their first real boyfriend, settled down, got married, then has children in what they thought would be a permanent, loving home.
This person was absolutely devoted to the family and bringing the children up as successfully as possible, hoping to follow the example of their parents in having a long monogamous marriage.
Sadly for them, when the kids were 8 and 10, having scaled down their career to provide the best support to the home and family, he being the breadwinner, his nibs leaves in the middle of the night, and texts to say he has left.
It later transpires that he's been having an affair with a colleague for six months, and that they have both left their families to be with each other. At first he said you can have the children and the house, I just want to leave and effectively disappears. He takes no interest in the children, causing immense hurt and trauma to the son. The only record of the relationship is pictures on social media, making it visible to everyone but the wife. He still denies it.
After a short while the other relationship comes out into the open, is admitted to. They move in together, set up a new rented home. Then the financial crunch starts - he withdraws support for bills one by one, cutting off the electricity, the phone, broadband etc etc. He keeps paying the mortgage and then insists that he is the landlord rather than it being the family home. And so on. He sees the children but has developed a self-justified, warped perspective where he is the victim, despite living in luxury while the family he left behind is on its knees. He keeps bitching about every aspect of their lives, criticising the mum for being "chaotic" while in fact she is running everything while he lives like a teenager again.
I know that it would be better for this person to accept it and "move on". But I can't for one minute think how. One day, maybe. The one thing I would say is that I blame him 100%, not the OW. But she will forever be the OW, and if I was in the same room as them I would struggle to contain my disgust at the way they have behaved towards his wife.