Although this is a very emotional topic, I do think these situations have to be evaluated individually.
I know that three or so years after my mother was diagnosed and when I had moved her near me in Ontario, my stepfather and I had such a conversation. In a roundabout way, he let me know he was lonely and wanting a relationship. I let him know very definitely that he had my approval, which essentially is what he was asking for. My mother was no longer aware of him as her husband and I felt, and still feel, that having him lonely and unhappy to conform to public opinion was not right.
The man in this case is visiting his wife in the NH two or three times a week. He hasn't abandoned her, he is still caring for her. He was lonely to the point of suicide, he says. Had he committed suicide, he wouldn't still be caring for his wife. If he were not still caring, I would feel very differently about his situation.
Love catches us completely unawares sometimes. To find love again is a great gift and it should not be blocked out.
Although I am not a religious person, I have always loved these two sayings attributed to Jesus "Judge not, lest ye be judged" and "Let he who is without sin cast the first stone".