Elon likes to play with words, and this could easily be that. In the original article, it said Sergey and his wife were separated, although still cohabitating

Elon likes to play with words, and this could easily be that. In the original article, it said Sergey and his wife were separated, although still cohabitating at the time, so you could technically say that she was not "fooling around on him." Likewise there would be no legitimate reason for Sergey to toss out his friendship with Elon over it if it did happen. At least not for the long term. But it is clear that Elon is not the reason for the separation, although some media outlets originally made it sound that way. Elon's statement about being too busy for affairs is laughable though, given the number of babies (that we know of) he's been spawning around the world. He's an all out rock star in the after hours.