Lawyer here - I actually would bet this is not the case. Whether he came clean or not, the 2nd affair with a subordinate is basically always a firing offense under the sexual harassment and/or code of conduct policy, whether you are a CEO or not.

If you didn't, you would be in for near infinite liability because it ends up as evidence that the culture from the top was tolerant of violations, etc. THis is not conjecture, it's what has basically always happened in the legal realm when companies try to work around it.