I would also suggest that you limit your conversations about your dad with you mother
If circumstances allowed, I would. Alas, they are still married, though she's leaning very strongly towards divorce right now. And her dementia will prevent her from being able to navigate the divorce bureaucracy. I go to her house once a week to pay her bills and check on things and do little chores. He often calls while I'm there. She then tells me about the call.
And any time he calls her and it upsets her, she calls me.
I doubt I'll be asking about him anymore though. But I can't avoid the topic without leaving her in a lurch of confusion, anxiety and agitation.
Interestingly, this morning I don't feel upset. Perhaps it's shock or perhaps it's acceptance (sometimes I can't tell the two apart initially). I simply feel as if the inevitable has finally happened, the shoe that I've been waiting to drop has finally dropped. It is what it is.