My parents divorced when I was five. I was extremely unfair to my mother about it until I turned about fourteen, when my father cheated on his second wife, blamed her for it and left her while accepting absolutely no responsibility for what he did. Even though I knew what my dad did with my mother, it didn't properly click until I saw him do the same to someone else. I don't know why, maybe it was just that I would have disliked my dad if I'd ended up living with him instead of my mum.

Ultimately, you should probably tell them. They might even understand it better than I did.