Yes. Unreliable by having an affair.

Not because he had an affair (who cares, really, and hardly uncommon), but because he had an affair that endangered the company, and in some respects our country.

Functionally, it's not different from "left an unlocked phone at a bar". A mistake anyone could make, but, when you're paid what he's paid, that type of mistake is the thing you're paid not to make.