Read Anna Karenina sometime. Tolstoy shows both the aspect of a society in which rich men having affairs was considered the norm, and the destructive effect it has on people. (And also the double standard by which women were judged much more harshly than men for having affairs). And he also, by comparing the two main relationships in the book (Vronsky's affair with Anna, and Levin's marriage to Kitty), said "It doesn't have to be this way, you can have healthy relationships if you just reject society's advice to have affairs and instead stay faithful to your wife".

I didn't like the book when I first read it (mostly because I seriously dislike Anna, and the book naturally spends a lot of time being told from her POV), but in retrospect, it's brilliant. Tolstoy has, without a single bit of moralizing, presented one of the best arguments I've seen in literature for being faithful to one's spouse and not engaging in affairs.

P.S. I should add that I don't think Tolstoy was inventing the "rich men having affairs was considered normal" aspect for the purpose of the book. I think that was what Russian society was really like at the time, and he took that aspect of society and wrote a book criticizing it, highlighting the negative effects that that attitude would have on people.

Do you really think it was never the norm for rich men to have affairs? That's a very optimistic view of history, I wish I shared it.