There needs to be a whole pre-M course called, "The In-laws".
My MIL just told our 9 year old son that she and his grandfather broke up (20+ years ago) bc "Grandpa cheated on me. He was dating X when he was still married to me."
What did you say? I asked my DS. "I didn't know what to say, Mom."
Well I sure as hell know what I am going to say!