Dear Queenie,

I happen to know my father is cheating on my mother, and with whom. I have seen it for myself and I have proof. He doesn't know I know.

My mother doesn't deserve this and I want to tell Dad to choose between that other woman and us. I also want to tell Mom.

Queenie, what should I do?—In the middle

Dear In the middle,

It's not up to you to tell your father to choose between his family and the other woman. That is your mother's prerogative.

The choice you should be giving Dad is: Stop seeing the other woman or you will tell Mom.

Of course, there is always the possibility that actually Mom knows already and has chosen to ignore his behaviour. In that case, there is not much you can do except let him know you know and disapprove, for whatever that may be worth.