My view on why the PM did not dismiss him straight away is that the PM has had a chequered love life himself, thus it would be the "kettle calling the pot".
In which case you are wrong.
Having a "chequered love life" (

) is not a reason for a minister to be dismissed "straight away".
Ministers are allowed to have a private life, and have relationships within that private life. Whether they have one, two or a hundred partners is irrelevant to the performance of the role, just as it is irrelevant whether they are male or female, gay, straight or trans etc.
If this was a conventional employment, dismissing someone because they had a "chequered love life" (

) would lead to an open and shut employment tribunal case.
It
was a resigning matter because he had breached the guidelines his own department had issued on socialisation between people living in different households. An entirely different issue to his "love life".