My mum was a SAHM and I would be horrified if my dad expected her to go out and get a low paid part time job!
The OP isn't your mum. Your mum presumably didn't also have a load of paid domestic help and also had a relationship with your father.
At any rate, the OP's husband isn't expecting her to go to work. He obviously feels that he's been used as a cash cow for years (because he has). He would stop feeling used if OP basically just does a bit of work and contributes something. Could be salaried employment, could be housework, it doesn't matter. The point is simply that she should DO SOMETHING so that their relationship (for want of a better word) consists of more than him simply pouring money into her largely idle lifestyle.
Even if OP gets a job now (or even if she had one five years ago) her total earning capacity and pension is greatly reduced from what it would have been if she hadn't taken a career break.
Ok, fine. So the husband has suggested just reducing the hired help as another equal option. Walk the dog, do some cleaning and laundry. Is it really so difficult when you have six hours a day to yourself?
She's come on here asking us if we think she is unreasonable to refuse to make any changes and to expect her lifestyle to continue exactly as it had before, with the added bonus of her husband being in permanent penitence to her. She's not prepared to take any account of the circumstances surrounding his affair - namely that he had no relationship with his wife, and she didn't give a stuff as long as he kept pouring money into her lifestyle. She claims she needs to be at home because her 15 year old son needs her, and yet when the kid is actually off school sick, she still expects her husband to upend his working day so she can do her hobby.
I honestly don't know why the husband has put up with it for as long as he has.