I've seen this sort of story lots of times. They want to leave but they can't let go. For people like both of our ex spouses we were "their's". Mine was very possessive and controlling. What I thought at the time as protective.
On the other hand, you and I both know far more about what is going on with them than perhaps we should. You perhaps more than I as my son, if he is a conduit for information is only from here to there. I get information from mutual acquaintances and yes, do drive by her apartment from time to time to see if she's still stuck. It "is" on my way to work but there are other routes I could take and usually do.
Is she watching me? Hard to say but I assume yes. The sister store to the one she manages is across the street and historically she would be there regularly. Don't know if she is now or not. The house is on the main street, I'm fairly "noisy" on social media, heck she even knows where the spare key is and maybe even kept a copy.
I do wonder what her reaction will be when I do indeed form a new relationship. Fortunately there is nothing threatening that she can do (famous last words?).
You are a fair bit farther out time-line wise than I am. And you had to have regular contact with him because of the kids. From your past posts he certainly was controlling - he would perhaps call it "taking responsibility". When mine left 2 1/2 years ago, that was essentially the last I saw her.
But as you write, we are in very many ways better off without them than we would have been if we had "won". And they're not (partial speculation on my part). They largely seem to have followed the script we read about here. Will they hit "rock bottom" and "change"? Doubtful in your case. Remotely possible in mine. But despite so very far they have "fallen" there is always more down they can travel.
I know you love your kids and are there for them as a sounding board for them to talk to you about anything. Is it perhaps time to ask them to no longer tell you about their father?
On BD H52, W50 T27, M26 S21, D23 BD-9-Mar-16 D-15-Jan-18 Final-19-Apr-18 I am a storyteller. The story may do you no good. But a story is never for the listener. It is always for the one who tells
