Legal Question in Criminal Law in California

Re: Payment for information

Not if he learned the information legitimately and the information itself is accurate. If he sells information which he knows to be false he is committing fraud, but your question suggests that the information is accurate and I don't see a legal problem with offering to sell it to the cuckolded husband.

Someone who has information another person would want is not normally obligated to share that information (there are exceptions for people in certain types of relationships, like attorney and client, but I presume that these exceptions don't apply here). Since he is not obligated to reveal what he knows, he can offer it conditionally. There is no reason he can't make a cash payment part of the condition.

It might be unseemly to do what you describe, but there is no law against it.