That is true. The thing is though he has admitted to having a 13 year knowledge of this woman and giving her money. I know in my marriage my husband would tell me about any woman/person who needed help and we would decide together how to help them. The problem is his wife didn't know anything about this. You don't keep this kind of thing away from your wife unless there is something going on.
Every marriage is different, in terms of what each expects from another or what would be tolerated and what would not.
Even the latest accuser is very vague. She says that she sent him 60 texts in the last month, but is vague on what the content is or what his responses have been. She says that he sent her money, but doesn’t say how much or how often. A couple hundred dollars is nothing to somebody like Cain and it may not have been large enough that he felt necessary to let his wife know.
Without specifics, we cannot assume anything.