Well, I don’t actually know, but what I surmise is that since Laura is now a producer, and Jack is heavily in demand for films that require location shooting, her inability to leave LA with him was the dealbreaker. He didn’t leave her for Tanya, at any rate. They are still on good terms, and supposedly Laura even put in an appearance at Tanya’s baby shower, so no great tragedy there.
Which is not to say that the marriage might not suffer from Tanya being the rebound chick, high school crush or not; plus the fact that she fell pregnant so abruptly, almost as soon as they moved in together. But who knows. Whatever happens, I just hope it’s the best for the kid.