I always found this one a weird one...
My Dad pulled me out of a school where I was very happy when I was 9, saying he'd looked at my school books and felt the standard of education was poor. It was an odd time of year, in between Feb half term and Easter and he was adamant it had to happen within about a fortnight. He was so disgusted at the standard of education...I had a week to say goodbye, then I was getting moved.
Years later, we realised this was actually because he was having an affair, and one of my classmates' mothers was his mistress' best friend. We were quite close, play dates etc.
When we moved schools and also areas to new house far away from his mistress, he made it hard for us to go back, keep in touch with my old classmates etc. I never saw that specific classmate again.
I was at the new school for over a year,
in the new area and in a new hobby and became close to a girl in the year below me at my new school. We began hanging out together at the hobby for hours and our Mum's and her Dad all became friends. She came to my house to play and my Dad was asked to pick her up. Mum came along as she'd never met my Dad (he was too busy "working all the time").
We got to her house and her Dad (who as far as I knew my Dad had never met) greeted him, "hiya mate, didn't know you had a daughter!" and they were laughing and having a joke. I was really confused.
Her Mum made contact with my Mum after the playdate. To let her know that their next door neighbour had been having an affair with my Dad for two years, they had a baby together and they'd only realised he was already married with a child when we picked their daughter up from their home.
I have no doubt we'd never have found out if it wasn't for this couple.
So I'd been moved schools/homes/hobbies in an attempt from him to conceal his mistress. Only to become best friends with the daughter of his mistress' neighbours.
It sometimes blows my mind a bit. And yeah my Dad/the situation was awful.