I feel so sad that my elderly mum's best friend has abandoned her in her hour of need.

Yeah, I wondered this... !

OP, you hate Joan. It's clear from your posts. You've said she's never left alone with your mum, could she be feeling the hatred from you?

It all sounds so difficult.
I wonder if Joan has got quite old fashioned views about what's proper for men/ women ? Lots of elderly people have quite antiquated ideas that become entrenched eg not much speaking to men or being left alone with them!!!
It's quite possible Joan doesn't feel totally comfortable chatting to just your dad for those reasons, and when she visits she brings her husband- maybe she thinks it would be improper to come on her own!!!

but what upsets my dad the most is the way Joan seems to relish in telling my dad all about a new couple they have become friends with and then proceeds to tell my dad about all the new places they visit with this new couple. It is really upsetting my poor dad and he feels she is punishing them both for mum developing dementia!

OK - so Joan phones once a week but talks to your dad rather than your mum? Phoning once a week is more than most of my mum's friends do, TBH.

In Joan's defence, if what she has done that week is visit Cafe Ritz or whatever, then that's probably "all" she has to talk about. But your dad could suggest that Joan calls every 2-4 weeks instead, if he is getting nothing but pain from the calls.

Are you also clear about how your mum is treating Joan? Maybe it's not safe for her to pop round or have as much contact any more? My mother in law is the Joan in a very similar situation. The family don't like her (my MIL) very much and, when my MIL has been in touch about genuine concerns for their mum's safety, have been very dismissive, curt and rude to her. It was my MIL who first alerted the family to changes in behaviour that led to the dementia diagnosis, and I'm not sure the family have forgiven her for that.

The mother in this situation (let's call her Pat), phones my MIL multiple times and at all times of the day panicking about things going missing, claiming there are people in the house, accusing her son of stealing her bag, etc. Pat is abusive to my MIL, she's screamed and shouted horrible abuse at her about the stupidest things - my MIL setting up a regular supermarket delivery for herself (that's my MIL's delivery to my MIL - nothing to do with Pat), for example. It's also not safe for her to go round to Pat's house. Pat has started hoarding food, and will become very distressed if she serves food to guests that isn't eaten, but is serving meat well past its sell by date, bread with mould, etc. My MIL got a tonne of abuse from Pat's son when she raised the issue of food with him, and has her own medical problems, so can't risk food poisoning.

I think you need to put your feelings about Joan aside and look objectively at the situation. Is your mum still lovely and kind, or has her behaviour changed? Does Joan feel unsafe? Can you have a positive, kind and caring conversation with Joan about your mum to see if there's any way they can re-connect?

I wouldn’t make excuses for Joan - a quick visit once a week wouldn’t kill her. My experience is that a "quick visit" isn't possible. Even when you get up to go, all sorts of ploys are used to keep you there. You can't walk out mid-sentence.

Not making excuses for Joan, just trying to scotch this myth of a "quick visit".

What's a couple of hours once a week ? Surely your mums friend can spare this time . She's a fair weather friend really, only there for the good times.

She might want to remember your mum how she was.

Sorry to be so blunt, but this is utter bullshit. I was with my mother every day as she drifted into the long night of Alzheimer's, and I was with her when she died. I still remember the vibrant, clever, and funny person she was before dementia, and all the wonderful times we had together. In fact, as time passes, those are the most constant memories. We remember what we choose to remember, especially as time passes.

People have choices, and avoiding a loved one with dementia merely because it's a bit uncomfortable is deeply sad, and really not defensible.

Also, some people seem to think that a diagnosis of dementia means that the person is no longer there, no longer feeling, thinking, and responding, but they are there, and often very aware of changes in their environment, including friends who have abandoned them. And yes, abandon is the right word.

This has happened woth my mum and a couple of her “friends”. One in particular that she would holiday with, who now tells her she is going away and that my mum can come when she gets “ better”! I think it is such a cruel thing to do, to get mums hopes up. She very rarely comes to see mum, and after she has visited all she has done is ring me and give me a hard time saying I should give up my job/home/ pets to look after my mum, when i am at breaking point trying to keep all of the plates in the air! She is an absolute cow of a woman. Horrible.

I think that Alzheimer's is a horrible desase. It hard for the person who has it and hard on the family members who are trying to look after them. In your own situation it hard watching your mother with this and your father dealing with it on a daily bases.
Then your mother's bf Joan who you would have expected to call over and meet your parents out for a coffee ect is behaving like this.
When she calls to your parents it all about her life and what she is doing with the new couple of people she is friendly with.

Meanwhile your mother is aware that Joan has not been around and your father has to hear about how great Joan life now is. That's hard on him. I think that as some people get older they can become very selfish. They think of only of themselves and what suits them. Then they stay away from people if they are sick or have Alzheimer's. It like if they ignore things it will never happen to them. I think in some cases they don't want to acknowledge that they are getting older or that the same thing could happen to them. One of my friends mother's is around your mother age and she has become very like this.

I think that you need to get in contact with the Alzheimer's society and see what services are available in your father's area. Their maybe a day center that your mother could attend and it would give your father a few hours of a break. In your father's case he needs to get a regular break from your mother for his own health reasons. Make sure he is claiming any benefits he is entitled to also as this could help pay for a career or cleaner to make things easier.
I would keep in contact with the person you mentioned who deals with Alzheimer's in your parents area and see what services are in the area.

I would also try to mind your mother for a day on a regular basis and let your father go away for a few hours even it only to met a friend of his.
Does your mother have any other friends besides Joan that you could contact and see if they could met her at home or in a local coffee shop? What about your father's friends, does he meet them or could they call to see them?

It not an easy situation for you all and it's important to help your father out as much as possible.

People don’t always cope as we would hope. I would suggest to your dad that the weekly phone calls aren’t helpful and scale back a bit.

It is so difficult to understand their perspective at that age. My DM has lived opposite her old school chum and her DH for 60 years. They were like an aunt and uncle to us. The DH has now moved into a care home with dementia and the chum has a number of health issues of her own. My DM has not been to visit in the care home and finds helping her chum a real struggle. I don't think she wants to be reminded of the fragility of life and she also needs all her strength to manage her own needs at home even though she keeps pretty good health. I guess it will come to us all eventually.

I can see how upsetting it must be for you. Is it possibly part of grieving for her, as well as her fear of facing the same fate? Possibly she's trying to talk about happy things by talking about recent trips when she visits and this is what is going on in her life, so she's being self absorbed but not intentionally hurtful? Dementia terrifies a lot of people. She is possibly putting on a brave face? I know when my FIL developed dementia my grandparents (who are much older) were horrified and spoke of it only in a quiet whisper to ask DH how MIL was coping, then a swift change of conversation to recent outings and happy times so that we all 'kept out chins up'. The idea of dwelling on it and discussing the details with the spouse or attempting conversation with FIL that might reveal how much he was struggling would be considered very inappropriate by my grandparents generation.

Joan is scared to look at her own possible future.
And by telling your Dad all about her wonderful life and new friends she is confirming to herself that she is okay, that she is in control..
Yes she is heartless. Yes she is selfish. I agree.
But it sounds as if Joan has always been Joan.
I would encourage your Dad to distance himself from such a person. She brings no light.
Best wishes to you all.. this disease is a bastard.

Can your Dad meet up with the husband occasionally just so he has a social life still? I think some people just can’t deal with friends or relatives having a serious disease.

There it is again 'abandoned' if I was your mum I would be more upset by you seeming to make this about you than losing touch with someone, it all sounds very dramatic