@mummmy2017, the fact that Johnson was allegedly advised by Geoffrey Cox that the law allowed what he did doesn't mean that Cox got the law right. It's pretty clear that the reality is that Cox told Johnson what he and Cummings wanted to hear, probably with his fingers firmly crossed behind his back. The history of this Parliament is riddled with successful judicial reviews against government decisions, notably many involving Chris Grayling, and presumably some lawyer incorrectly advised the ministers in question that it was at least arguable that what they were doing was lawful.
Your analogy with smoking in the car with children is false. That is now against the law because the Children and Families Act 2015 made it illegal, not because of case law.
The simple fact is that, when a Prime Minister chooses to do something unprecedented in constitutional terms, in effect they have to be able to demonstrate that what they are doing is lawful - it's not for their opponents to come up with specific laws overtly forbidding it. Frankly, it was always obvious that proroguing Parliament for your own political advantage was unlawful: the reason there is no direct previous case law on it is because no-one else was stupid enough to try it.
What the Supreme Court has done is simply to confirm what has always been the case, i.e. that what Johnson did was against the law. It didn't change the law retrospectively as you seem to believe.
The fact that allegedly millions of people in the UK support a known fraudster and liar is, frankly, deeply depressing and shameful. If he is allowed to continue on his current path, he will not hesitate to throw each and every one of those millions to the wolves if they get in his way.