Did your in-laws stay in touch with you after you separated? My ex had an affair with a girl half his age but despite it all being his doing I've been dropped by my in-laws like a hot potato.
I used to go to their house every week, helped out with errands, sorted their admin, their internet, wrote letters for them etc. In 30 years I have had a cross word with my parents in laws or my sister and brother in laws nor any of their spouses. I've been an attentive aunt to their kids - remembered their birthdays, bought the birthday and xmas presents. Ex-Dh did fuck all in that area.
Ex-Dh is a grandiose narcissist and MIL is a covert narcissist (always the victim - hence all the letters I wrote for her for whenever she was "wronged" by various companies).
I was with him for 30 years and I've been absolutely excommunicated from their side of the family. MIL even bitched about me to my DC. I understand it from him and my MIL but I don't understand why my bro and sister in law and their other halves have also done that.