Adultery in itself is not really a resigning matter - although it seems a lot of the current ruling party have loose morals compared to the standards they hold others to.
Affairs with people who work for you are more problematic - there is a potential power dynamic issue, and of course a potential conflict of interest.
Affairs with people you appoint to made up jobs and then breach laws with that you create.... even this corrupt government couldn't ignore that.
And of course in yet another amazing coincidence the brother of his mistress has been given another of those sweet sweet Tory government NHS contracts. I'd be tempted to have a lusty affair with Hancock if that's the ticket to millions too.
And still the blind defenders of the cult will refuse to hold them to account.