I know I should leave, but I'd like to keep setting that bar higher during that time.
I am missing what you mean by "setting that bar higher"?
I did tell him I'd "like" to start dating others during that time. He didn't like it but understood that it was fair.
What man in their right mind wants competition? You should absolutely date!!!!!!
/u/memyselfandanisland really hit the nail on the head. Why would a childless single woman choose to take on a situation that at best has the cards stacked against you? I would really encourage you to read books, listen to podcasts about being a stepparent. Dear Sugars podcast (one of my favorites), had an excellent, well balanced perspective. If anyone ever figures out that you were in the picture prior to his divorce, you will be persona non-grata. Not to mention the very real reality that he may someday cheat on you. I also agree that you will be ultimately be financially supporting your new step-children, and perhaps more of the household finances, as he likely will pay spousal support, etc. I personally think things will become a whole lot less sexy and fun.
At this stage in your life, when you still have the chance to find a man without children, and who hasn't been married, why wouldn't you jump at that chance?