Seem to have lost my motivation

Yes. Regularly. I also have arthritis and am now 77, caring for my DH. Have put weight on because even when we go for a walk I have walk slowly for my DH, and though I do try to no out for a quicker walk without him sometimes I am usually too pooped to go far.
So yes I do tend to think ‘to hell with it’ and want to devour a box of chocs in one sitting. I don’t btw.
But you are not alone in this.

Sadly, for many of us with progressive conditions, this seems inevitable.

Take your time, try not to get frustrated and do whatever you can manage.

Allow yourself little treats without going mad, but who wants five extra years in the nursing home?

You're definitely not on your own Travelsafar, I've been there.
There's a way of thinking called CHIME, which my daughter introduced me to where
C = connection
H = hope
I = identity
M = meaning
E = empowerment.

She's a clinical psychologist who uses it with severely mentally ill people but there's lots of research to show that thinking how to improve each of these different aspects of life helps people facing all sorts of difficulties including divorce. bereavement and chronic illness.

There's lots on the internet about it and there's a thread on Instagram called @chimerecovery which I must add, in the interests of transparency, is run by my dd.

It's definitely not a magic wand, takes quite a lot of time and effort but it's helped pick me up so I feel it's worth passing on.

I forgot to say that my dd is just setting up the Instagram page. She's done a lot of research, particularly into how CHIME can help people older adults (I wonder why!) and one of the interesting findings is that it can not only help to improve psychological wellbeing but boosting connectedness, hope and meaning are also associated with better physical health.

Yes, OP, I feel just like you.

I am 78 with arthritis steadily making its unpleasant way through my body. I also have a rollator and attend lots of local groups.

I was sent on a pre-diabetic course 18 months ago and I did my best to stick to the eating plan and managed to lose just under 2 stone. However, I get cheesed off with looking at appetising things in the shops but think, best not.

I fall by the wayside occasionally as I am only human but I don't beat myself up over it. Treats now and again don't hurt and are good for morale. After all, over 70 is not for sissies. We deserve a goodie sometimes.

Yes, I think it's a normal part of ageing (which we can't outrun, much though we'd like to believe the Everlasting Youth promises churned out by magazines and ads). You won't get obese from the occasional indulgence (nor spend an extra five years in a nursing home!). Plan to give yourself one treat a week (you can have a couple of lean-eating days beforehand to compensate for it). Two days gently cutting calories, one day eating what you like, four days being sensible - sounds like a balanced plan to me.

Why don't you cut your treats down to just a small piece after meals? I love Cadbury's chocolate and can overeat on it. Now, I just have one small piece after lunch and really savour it. Perhaps use a dessert plate instead of dinner plate which will make your portions smaller. Eat the same food but reduce the portions.