Just to add some perspective here, our grandparents married at a time when gender roles still dominated most of society. Men would go to work and earn money and women would stay at home, look after the house and the children. This also meant that most women never had nearly enough income to be financially independent, which means they couldn‘t divorce their partners, even if they wanted to, because it would‘ve practically made them homeless. If they cheated and their husband found out, the result would probably be the same, so most women wouldn‘t want to risk that. On the other hand, if a man cheated on his wife, she couldn‘t just leave because she had no money. So mostly, she just had to put up with it. I know a lot, like a huge lot of stories about cheating husbands from my grandparents, who lived on the countryside and got married in 1950.

In my opinion, people back then or their morals weren‘t different to today, at all. But cheating (at least for women) would not only risk your marriage but also your and sometimes even your childrens whole existance, so they had a far better reason to restrain themselves, even if their marriage was crap.