I know we shouldn't judge anyone, male or female, on their appearance alone.

But when you don't know anything about their personality, level of intelligence or any other qualities then it's sometimes all there is to go on.

So I reckon Boris Johnson's wife Marina Wheeler is too good-looking for him. And I don't know why she didn't divorce him years ago.

Cynics suspect that it's happening now so that by the time he makes his move to oust Theresa May the divorce will be behind him, it'll be old news and it won't hinder his prospects. People have short memories.

But his wife has long had grounds for divorce.

Johnson - and I refuse to call him "Boris" as if he's a friend of mine - has given her plenty of reasons to ditch him during the course of their 25-year marriage.

He got into trouble when he lied about an affair with journalist Petronella Wyatt.

He dismissed the reports as a "pyramid of piffle", until they were proven to be a pyramid of truth and Michael Howard sacked him from the shadow cabinet.

According to some reports of the affair she fell pregnant and had an abortion.

One woman who didn't have an abortion, and bore Johnson's child, was art consultant Helen Macintyre. He had a daughter by her, born in 2009.

That affair came after a relationship with another journalist called Anna Fazackerley.

And those are only the ones we know about.

Some will argue that this is all irrelevant. It may be wrong, and a shabby way to treat his wife, but it doesn't necessarily impinge on his ability to do his job - or Theresa May's job.

Bill Clinton's extra-marital activities were well known and when his vice-president Al Gore ran for the top job it was said that he'd be a safe pair of hands, and a safe pair of trousers.

But he didn't make it, while Clinton was elected twice.

Francois Mitterand's 32-year affair was widely known about, and resulted in an illegitimate daughter. And yet he was France's longest serving president.

And our own next head of state is likely to be self-confessed adulterer Prince Charles.

I suppose it's only really wrong when there's hypocrisy involved.

It was in October 1993 - almost exactly 25 years ago - that John Major made his famous finger-wagging declaration at the Conservative conference: "It is time to get back to basics."

It was taken as a plea for traditional family values. Then came the news of extra-marital affairs by a string of Tory MPs, including David Mellor, Tim Yeo, Rod Richards and Piers Merchant.

Junior transport minister Steven Norris was conducting simultaneous affairs with three different women, who didn't know about each other.

The wife of Tory peer the Earl of Caithness committed suicide when his affair was exposed.

At the time it looked as if the well intentioned but accident-prone prime minister was being let down by his colleagues - until Edwina Currie revealed that Major too had had a four-year extra-marital affair, with her.

Or there was former DUP MP Iris Robinson who was ever ready to denounce homosexuality, saying: "The Government has a responsibility to uphold God's laws."

It turned out she was rather more lax about one of God's other laws, the seventh commandment that "thou shalt not commit adultery". The married MP, who was 58 at the time, had been having an affair with a 19-year-old butcher.

Johnson may not have been moralising like Major and Robinson. And marriages do come to an end.

If a spouse is violent or abusive or adulterous, or a couple are just incompatible, then they should be allowed to separate.

But Johnson's adultery is a problem because it shows that he's untrustworthy. That's not a good quality in a politician, and far less in a prime minister.

If he can't keep the promise he made to his wife then can he keep his promises to the electorate?

In any case it's well known that he's only a recent convert to the Brexit cause.

He wrote two newspaper articles, one arguing for remaining in the EU and one for leaving, before deciding that backing Brexit was a better career move and publishing that one.

Theresa May isn't as "strong and stable" as she claims to be but I reckon she's more stable than Johnson. So I hope he doesn't succeed her.

He may end up doing to the country what he's done to so many women.