Yes, I was just 14, my db was 12
Completely out of blue my dad didn't come home one night. No one was aware of any problems, including my mum. I never heard them argue once, about anything..
I can't remember how, but found out he was ok, but still remember holding my mums hand in the window watching for him to come home.
Turned out there was another woman, but he never spoke to mum again, all contact through letters.
My mum, to her eternal credit, always facilitated and encouraged contact, although my db never forgave him and went off the rails for a while. He desperately missed his dad, and took out his anger on himself and us.
I was so busy trying to look after mum, taking over her role and trying to do the 'dad' jobs too, whilst she broke apart. I never got the chance to grieve or get angry and this has had a lasting impact on me. Late 40's now.
Family and friend were all incredibly shocked, he was such a liked and gentle person, and none of us had a clue. He never contacted any of his family or his friends again either.
My db and I saw him for about 4 weekends a year, he gave mum the house and paid maintenance.
Once he left he backed away from the role of parent, maybe he thought he had forfeited any rights, but that left all parenting to mum, very fragile. It also meant that we lost parent/child relationship closeness too.
I still miss it.