Seems it depends what else he/she has going for him. According to this article in the Daily Mail one wealthy Surrey housewife has decided to stay with her husband as she cannot give up the lifestyle.
Methinks they interviewed her too early. Even if she divorced him, it appears she would still have a lifestyle in excess of what she could have attained on her own steam without him.
Lots of people choose money and misery. Even more people choose money and misery initially. People do not seek happiness, they seek the least unhappy choice. Only when they get to the stage of realising that the status quo is the most unhappy option do they choose to leave.
For some it is a lifestyle choice. Some people regret staying married, some people regret getting divorced. I can think of a few high profile celebrities who have gone off the radar since their divorce, mentioning no names but they have gone to extremes as far as self promotion is concerned and they are still ignored!
If you are able to forgive your partner and move on then staying married may be the right option. What is important is to work out what you want. Implementing it is not easy but at least you are working towards your dreams.
What do you want?