I used to get on very well with my husbands ex. She referred to me as her children's second mother, and at family events for the kids, we would often sit together and chat happily. We would speak on the phone if there were problems with the kids when they were teens, and as there was still a fair amount of animosity between her and my husband, I was the one in the middle who could smooth things over..
Roll on to the kids having kids of their own and she turned into the psycho ex wife from hell. We havent spoken for 3 years, and I didnt go to my stepdaughters wedding last year because the atmosphere would have been so bad due to her behaviour. She chose to move 100 miles away from everyone, yet hates me because I get to see her grandchildren more than she does...
... and to give another example of her mental behaviour.. my adult stepson had an accident a couple of years ago, which meant an operation and a few nights in hospital. She went beserk because he rang me to ask me to take him to the hospital, and sent him a text saying if he allowed me or his dad to visit him, then she would no longer consider him her son.. but she didnt bother to come to visit because she didnt have time...
She is a really nasty, devious piece of work, and after spending a few years thinking that my husband thought that of her because well, she was his ex, etc.. and he was maybe over exagerrating it, I can now see he was absolutely spot on. She is poison.
(I met him 8 years after they had divorced, and she was remarried then too, so definately not a problem with me being the other woman who took her man).