This hasn't been my experience at all. I don't usually have Sims cheat, but it has happened on its own twice in my game. The first time, it was at the wedding. The groom's father flirted with the bride. The groom became upset and got a moodlet about unfaithful mate or something like that. But there was no reaction toward either his dad or bride. He just got angry. He even went through with the marriage...as I had queued it up before all that took place.
The second time was when I had switched houses. There was a lady that kept knocking so I finally decided to let her in. I didn't realize that the hubby...same guy that flirted with his son's bride...had a fling while I was away. So the guy, fling, and his wife were all in a conversation together. The husband kept flirting with the other woman and his wife was just like...whatevs. She just carried on the conversation like she was completely oblivious. Then I forced the husband to flirt with his wife and the other lady got mad. Since their marriage was destroyed in my eyes, I decided to make the guy woohoo with his fling. His wife didn't bat an eye. Then I thought maybe she had to be in the same room so I had her walk in on them. She got embarrassed, not because she caught them cheating, but because she walked in on them. I gave up and just made her be mean until they got divorced.
Also...she had the family trait. So if anyone should be upset, it should be her. They were elders so that's like a lifetime with her spouse.
