I don't care at all about the identity of the subordinate - just whether or not it was consensual and if there was anything that could be perceived as harassment or abuse, before after or during the affair. If he followed up with that incident with a separate affair with an owner's wife, the fact that it was an owner's wife makes all the difference, and there wouldn't need to be any harassment involved to make it a fireable offense .
Consensual or not you don't sleep with your boss's wife, and while that may not be some type of moral issue it's just common sense. The owners hire and fire - piss them off like that and you are getting fired. And this was after he was already told to calm it down. If an employee somehow doesn't get that you can't do that, it just speaks to their inability to control themselves or understand proper boundaries - something that could obviously affect their ability to be a leader in an organization.
First, to be clear, I was not responding specifically to your post. "Whose wife did he sleep with" has been a theme since this thread started, and it has bugged me from the start.
Next, it may be common sense to not sleep with your boss's wife, but I think this comes from an old-fashioned way of looking at things. We don't know what happened or even if there is anything to this recent rumor, but suppose there is. What if the woman lied and told Ime that she and her husband have an open relationship? To what degree would Ime have any responsibility? The event could lead to a divorce or marriage counseling or other things between the husband and wife, but without knowing more about what actually happened, it is not clear why this should have an effect on Ime's career. If X's wife slept with Ime, who knows, maybe that says more about the relationship between X and his wife than it does about Ime.
Parts of this discussion have the vibe of men thinking about how they would feel if they found out that their wife had been having an affair with Ime Udoka, and I am suggesting that this is not relevant in determining what happens to his job or his career. What matters is whether it was consensual, whether there was harassment, what the company policies are, whether the women were employed by the Celtics, how Ime's behavior could affect his job as head coach, etc.
Finally, identifying someone as "X's wife" bugs me. There is a long history of referring to women by specifying their relationship to others — so-and-so's mother or wife — much moreso than men. Old-school 70s feminists critiqued this, and I think we should be able to finally listen to them and avoid this old pattern.