I suspect it is true and Boris hates being PM because it's too hard and he's expected to work, plus he's used to having far more money.
However the stuff about child support is blatantly about the story everyone wants to write about but can't, however is easily findable on twitter or google.
Hadley Freeman was cheerfully alluding to it in her Spectator column - 'unmentionable gossip about Boris' which she then decides to talk about about 4 times without telling us what it is.
The right wing press billionaires are fed up. Murdoch wants Gove in, as if that will magically be any better. There will be masses of negative stories about Boris from now on.