If you are willing to have an affair with someone else's spouse, especially when that person has been a mentor and championed you by promoting you, you're probably pretty devoid of any loyalty or moral fiber. And then to refuse to leave? Yeah, you can assume that person is completely untrustworthy in any regard.

Note, I'm not referring to a single mistake in a moment of weakness but an ongoing affair.

I get the tautology that if you can't be trusted then you can't be trusted, but I still don't see any reason to believe this would extend to something like theft.