To be honest. I can see how this happens.
The intimacy slowly goes, no one discusses it, the kid is young and she has help at home, the kid grows up and she starts to develop her own life outside the home, happily plodding along in her own bubble, where he does his thing, she does hers, and they come together to be parents or meet friends,
She then gets bam, he's been having a long term affair , bam he's not happy with her level of contribution and her life needs to change and she doesn't want to, bam he's not happy with the relarionship.
She doesn't want to sleep with him, she doesn't want to do more household tasks, she doesn't want to get a job, but she wants the status quo to remain, she wants the life she had built up.
However that only works if he wants it too. So she needs to compromise. Start doing more round the house, or start selling her paintings and turn it into a business, or get a job, or she needs to accept the marriage is over and her life will change anyway. The lady of leisure is over.
I suspect she only wants to stay married due to the security of marriage, the social standing, not wanting to be the single woman, not wanting to live alone.
The question she faces really is would she rather be alone and divorced than make the comprimises he requests. Because either way she is going to be making changes. Which ones are up to her. I actually feel sorry for her, because she doesn't want any of it, the issue is she's acting entitled to her life and unfortunately she's not, because it's him that's providing it.