Funnily enough, although I have read probably 95% of his books, I've never really bothered digging into the complicated personal life of Robert Heinlein.
I see that it was summarised in this post at io9 in 2014, which I may have missed. Strangely, it seems he was clearly on the Left of politics prior to World War 2, then moved to the libertarian right with his second wife. But both marriages were (apparently) open, with the first one including a 3 way relationship with L Ron Hubbard for a time (!)
He really was a very odd character.