Vancouver guy. Runner and adventurer.
First off, I’m very sorry to hear that your mother suffered from a stroke. I’m glad to hear that she has recovered well.
Take your bf’s word for it, it sounds like the guy knows what could happen and that he knows how to deal with it.
My friend has a FTM boyfriend and so her mother recognized me as being FTM (she has an eye for it apparently XD) and told the father. When I met him he asked if I had a “pecker sewn on”, which was essentially another way of saying “have you gotten dick surgery?”. She and her mother were mortified. I was fine and I joked with him a little and he ended by saying “I didn’t mean it man, thanks for being a good sport”.
Point of it is, they were more offended than I was. The way I saw it, he was being quite personable to me. A little thing like an off-colour joke wasn’t anything that would make me question my masculinity because in the end he was treating me like a guy anyway.
In your mom’s case, it is truly not her fault and any pronoun mistake she makes can simply be chalked up to an effect of her condition. If she calls him “she”, it can equated with your mom calling your dad “she”. if she calls him “he”, then that’s that. That’s how I perceive this anyway, I hope that helped!
Best wishes to your mother, boyfriend and to you! :)