FOR ONCE I want him to make a fucking decision.
I think he's deciding he wants cake. He's keeping you as his plan B & acting like a single guy.
Protect YOU and YOUR children. Like others have said, if it takes a year, you can stop the process IF he starts to get it.
I understand your thought that he's going to snap out of it (at some magic point in the future). I did the same w/my XH.
All the delaying on my end first (his later) was allow OW to get her claws deeper in, fill his fool head w/even MORE nonsense & reinforce his selfish, entitled attitude. I wasted those YEARS hoping & praying for a magic moment when I could have focused on moving forward instead.
I wouldn't give him any notice of your plans at all. I would file on Monday, and look toward a future without your H.