I have name changed for this as it is outing.
My DM & DF split when I was 7. DS was 9 and DB was 6 months. DF had been cheating. He left instantly when DM challenged him and went on to marry his mistress and have children with her. Still together now, 40 years on. We lived with DM and DF continued to see us EOW. The other weekend we went to his parents, who we adored. However DM hated him. She still cannot hear his name said, 40 years later. She insults him still, on the rare occasions he is brought up. She made his life hell during the first few years and moved in with a new boyfriend (still her DH 40 years later and overall an amazing man and dad) after 6 months. We were all told to call him dad instantly. She demanded that DF not let us near the OW (his new wife). With them living together this made it hard for him to see us. Within a year she began to make it difficult for DF to have us. Being vile to him and also getting her DH to be aggressive towards him by telling her DH lies about DF. DF eventually gave up and stopped seeing us. He continued to pay maintenance. To be fair he never visited us when we were at his parents, which he could have. His DW was nothing but lovely to us. She and DF never once spoke badly of DM & DStepF. His DW used to ask me how my mum was whenever I saw her. Yet DM still cant hear her name and if you mentioned her you either get "what did that slag want?" or "oh why dont you just go live with her then. shes sooo amazing". After the divorce DM spent the next 40 years spitting vile hatred about him every chance she got. We have constantly been told he didnt want us, he chose his new wife and children over us, he never wanted us etc. If you bring him up she is truly awful and we have heard the stories over and over about all the things and lies he told her while cheating on her. These are stories we heard as young children onwards. we have all privately spoken to DF, since being adults, but he is not part of our lives. Mainly due to the hatred that DM would spew about it. If we see him she ignores us for weeks.
DS was 9 and is most affected. She was told from day 1 that her DF had left, didnt want her and she was to hate him. She is a people pleaser and desperate to be loved. Cannot stand it if someone falls out with her. She cant keep a relationship. She has a fear of marriage and children. She is amazing in her field of work and is constantly looking for praise and to be the best. She can see how vile DM is (not just about DF but everyone) and excuses her behaviour. DS has spent thousands on therapy over the years and knows WHY DM acts like she does but still enables her. She wants to fix things. DM has been horrible to her over the years (including ruining her wedding by flouncing out as she felt she was being ignored) but DS still lives up DMs arse.
DB was not affected by the divorce and words as much as he was 6 months old. He had DStepF as his dad and adores him. Theyre very close so he hasnt missed out. DM attempts the "your dad didnt want you" stuff on him but DB doesnt really care as he doesnt know DF and has a dad already (DStepF). However he never lets anyone get too close. This may just be living with DM though as she is damaging.
Then me. I was 7. I remember it all but Im a bit different. I always chose to do the complete opposite of what DM said (just to annoy her). I believed what she said but I didnt really care. I just remember hating HER every time she said it. Even now. I have a cordial relationship with DF (for my grandparents sake) and I dont really care if he is around or not to be honest. I dont want a relationship with him as hes a stranger and I also dont want my children to. We have a "dad/grandad" already with DStepF. We all prefer him to DM to be honest.
So in short I think divorce is ok, its how its handed afterwards that does the damage. 3 children damaged by his actions and her way of dealing with it. My DF is a nice person (who made a bad choice of how to do things), my DStepM is a lovely person and so is my DStepF. It could have all been avoided if DM hadnt been such a bitch. I do think even if DF had left her THEN began the relationship she would have treated him the same as she does now.