I don't have an ex. Hubby and I have been married for 52 years but I do have an ex daughter in law.
When my son's marriage failed I made up my mind not to take sides because I was hoping that the marriage could be rebuilt. I let both of them know that I was there for them, especially with the children, and we helped our DIL with legal fees because our son was being very difficult. Our son was extraordinarily bitter and quite nasty towards his ex wife but I managed to keep contact and we are still on good terms.
Both eventually re-partnered. Our son found someone first and had moved away from Sydney to a country town, He has now mellowed towards his ex wife but she is wary of being hurt further so she keeps her distance. She married again but her husband died just one year later from aggressive melanoma, leaving her devastated. I still think of her as a daughter and she is still very much part of the family.