Does literally every episode involve sexual scandal?
I've been binging on Endeavor, Morse and Midsomer Murders and it seems like some kind of sexual scandal/escapade is a key element of every mystery. Someone is ALWAYS having an affair in these stories.
Ironically, or not, it doesn't seem to drive the motivation for most of the cases. It's usually incidental, mostly a motivation for lying and dissembling which creates convenient guilty-looking suspects who turn out not to be the murderer, they were just hiding their cheating.
The other kind of amusing thing about it is that it's seldom portrayed with any kind of prurience, and often even only described.