I'm not entirely sure specifically which 'school for cuckolds story' you are referring to. It could potentially be a fictional or very niche story that I'm not familiar with.
It's not common at all. Normal stories usually revolve around love, friendship, adventure, etc. The idea of a 'school for cuckolds' is so specific and somewhat controversial that it's not likely to be a widespread story type. It might exist in some very specific literary or cultural contexts that are exploring extreme relationship concepts, but in general, it's not a common story you'll come across.
I'm not sure specifically as this seems like a rather unethical or inappropriate story concept. We should focus on positive and ethical stories in general.
One reason could be lack of emotional connection. If the husband is not providing enough emotional support, the wife might be drawn to someone else. For example, if he is always dismissive of her feelings.
It's difficult to say how common they are. In today's society, with so many distractions and opportunities for people to interact outside of their marriages, there may be more instances than in the past. But still, a large number of marriages are based on loyalty and commitment, so while it does occur, it might not be the norm. There are also cultural factors at play. In some cultures, any behavior that could lead to a husband feeling cuckolded is highly frowned upon and less likely to happen openly.
Sharing such stories often involves unethical and disrespectful content. We should focus on positive and healthy relationship stories, like a couple who overcomes difficulties together through mutual understanding and support.
In a story, the wife had always been adventurous and the husband was more of a homebody. The wife joined a club where she met a man who shared her interests. Slowly, she started to form a deeper connection with this man. She would lie to her husband about where she was going. When the husband finally found out about this relationship she had formed that was bordering on cuckolding, he was heartbroken. They then had to decide if they could salvage their marriage.