-Removed-Like most things, it depends greatly on the circumstances.
I use to work in a day centre for people with Alzheimers. I remember one poor chap (a husband of a patient with the condition) who felt terribly guilty because he had started a new relationship with a women, although continued to be a carer for his wife.
Technically he was committing adultery, as was still married, but think it would be a very cold person who questioned his morality.
An extreme example perhaps, but as i say, things are rarely black and white.