He is married with children. She is married with children. Relationships break down, we all know that. But moving on to the next one before you've ended the last one is appalling behaviour. Having an affair which you hope to keep secret while you pretend all's well with your marriage is even worse. It shows you are a callous, dishonest person with poor self-control and you can't be trusted.
Boris Johnson has done, and therefore is, all of the above. He is in no position to criticise Hancock, never mind sack him on moral grounds.
If Cummings is behind this, it's quite clever, as it shows Matt Hancock in a very bad light, but even Johnson's biggest fan can surely not avoid seeing the parallels here. Cummings must surely know he will never be re-employed in government, and he seems to have decided to bring the whole pack of cards down with him.
The pretext for sacking Hancock now would have to be breach of Covid regulations. They got rid of Professor Neil Ferguson on those grounds. Was that Cummings' work too? Shows an established MO if so.
Of course, if the affair started before she was appointed to her post, that's an open and shut case and he should be sacked for that alone, but there again - remember Jennifer Arcuri? Johnson once again has already done similar.
I can't tell you how much it galls me, as someone who really ought to be voting Labour, that Her Majesty's Opposition is in such disarray that our current dishonest, incompetent, morally bankrupt government is seen as the less awful option and so seems set to remain in power for the foreseeable future. FGS, Labour, get your act together and re-connect with the electorate!