For those who think cheating is always wrong, I have a question.
Imagine you have been married for 5, 10 or 20 years and your wife is no longer interested in sex. Maybe she will do it once a week, or month, or year or never.
Do you think that because you once said "I do" to someone that for the rest of your entire life, they and they alone get to decide when you have sex. If they deny you sex, you can't have any? Does that sound right? It doesn't to me.
This happens all the time. Women become less interested in sex as they get older. Men are less likely to have as big a drop off in sexual interest. It's a pretty silly arrangement that men agree that someone else gets to decide if they are allowed to enjoy probably the greatest thing in life.
I think people should do the best they can to meet the sexual needs of their partners. If your partner is willing to accommodate, then cheating would be wrong. If one person in a relationship is unwilling to do that, then I see no moral dilemma with cheating.