Lisa, thank you for such a wonderful, heartfelt story. By the time my first wife and I broke our relationship in 1980, my parents and hers had become best friends and their relationship lasted well into this century, with frequent visits to each other. I also visited my ex-in-laws from time to time, but not my ex.
I know ex-partners who have not kept contact with their respective ex’s parents. because it was too painful — they said they needed to make to break a clean one. However, I can feel your loss and it is real.