Suppose after cheating on a test you wind up succeeding anyway. The company isn't harmed and in fact you wind up doing a stellar job despite your dishonesty. Can you still claim that it was absolutely wrong to cheat on the test when society has benefited from it?
There will always be outliers in a distribution of life.
If someone cheats and gets ahead and does something productive but its is not the norm, then society will still pressure people to not cheat as it would be the better option. If your argument is that cheating is a net benefit, then society would not likely condemn. We dont live in a world where cheating benefits the overall population so I cant really go too much further into that. But, yes, cheating will benefit the individual if they are not caught, and harm the majority of people around. Sometimes that is not the case, but typically it is. So cheating is still immoral and still does not need religion to explain that.
Suppose your spouse cheated on you first. Suppose the marriage is already hopeless, but you haven't yet pursued the divorce. Do you still consider yourself bound by your wedding vows?
Yes. Say my spouse cheated on me, and I then cheat on her. Its likely to get around that I cheated too, which would dissuade other potential mates. Who wants to enter into a long term relationship with a cheater right? So again, culture would be benefited by condemning cheating.
You seem to be stuck on this idea that if it benefits the person, that society would not condemn it. Cheating, lying, stealing all benefit the individual in most cases, but hurt the society over all. Take Africa as an example. Most of Africa has enough people and resources to make life better. A big problem is nobody wants to invest if it will get destroyed or stolen. It is stuck in a violence and corruption trap. People tend to spend what little they have because they may not have it tomorrow.