Up until recently, I would have said that infidelity is both immoral and disrespectful. Then I adopted the view that it was disrespectful but not immoral (if it could be guaranteed that one's partner would never find out about it) and now I'm not sure it's even that much (disrespectful). Imo, something is morally wrong if it either a) causes someone else to suffer or b) deprives them of pleasure/happiness. Cheating on your spouse, if it could be guaranteed that (s)he will never find out, would not cause him or her to suffer nor would it deprive him or her of pleasure/happiness. His/her preference to be in a monogamous relationship would be satisfied, irrespective of whether or not they actually are in a monogamous relationship. The standard argument against cheating is "I wouldn't want my partner to cheat on me or to keep it from me" but this is actually a nonsensical thing to say and I think it comes from our highly developed capacity for abstract thinking. If you did not know that X=Y then it's meaningless to say "If I didn't know X=Y, I would want to know that X=Y", it's not as though you would be sitting there thinking " I wish someone would tell me that X=Y " or "I wish X did not equal Y". What exists to you is what you consciously experience. At the very least, I argued, it was disrespectful but to 'respect' someone is to hold them in high esteem. People do not cheat because they have a low opinion of their partner or because they are dissatisfied with their relationship, although I'm sure both justify cheating to someone who themselves believes that cheating is unethical and/or disrespectful. Bob has sex with Jill because he is attracted to Jill, not because he lacks respect for his wife Elisabeth or is dissatisfied with their relationship. I feel that it's tacky to lie to someone you care about but I can't actually articulate why it is disrespectful or why honesty is a moral virtue in circumstances where lying wouldn't alleviate suffering or cause pleasure/happiness. I just don't see how you could lie to someone and be truly intimate with them. If nothing else, I think cheating is morally irresponsible for the simple fact that you cannot guarantee your partner will never find out and it wouldn't be worth the risk of causing them distress.