Well, it's hard to say if they are common. Some might accidentally end up in a situation that could be considered cheating due to miscommunication or being in the wrong place at the wrong time. For example, a person might go out for a friendly drink with a co - worker and things get out of hand after too many drinks.
No. Such content involves explicit and often non - mainstream sexual themes that are not suitable for mainstream literature which usually adheres to certain moral and ethical standards.
No. Such stories are often highly inappropriate and involve private and sexual content that is not suitable for public sharing. It violates social and moral norms.
No, it is not ethical at all. Cheating in a marriage is a betrayal of trust, and having an interest in watching stories about it is rather voyeuristic and disrespectful to the institution of marriage. It also shows a lack of respect for one's partner and the commitment that marriage entails.
No. Watching stories about cheating in sexual relationships is not ethical. Cheating involves betrayal, broken trust, and can cause a great deal of pain to those involved. Promoting or being interested in such stories can also have a negative impact on one's own values and how one views relationships.