My exh has a wife and young baby. His wife is not happy with teen step children. His marriage looks rocky and he says "things are bad".
My DH's ex left him for someone at work. She seems happy.
I do think both are determined to stay with OW and OM. They re married later than we did (my hubby and me) largely because they broke up with the OW/OM and then got back together.
My DC would be (naively) 'happy' if their Dad's marriage fails because they hate the arguments, but they get very distressed at the thought of not seeing much of the baby. He talks this through with them - and I don't because I have little inside info!
Have your ex's marriages/relationships lasted with OW or yours with OM?