When his wife finds out the extent of your intimacy together, she is going to toss him out on his ear (or at least she should). To have that lie, on top of all of the other lies, is likely to be the last straw, kids or no kids.
The same may very well happen between you and your husband, y'know.
His kids are well aware there is or at least was something going on. Unless they are profoundly developmentally disabled, then they know or at least sense something.
And so do yours.
Blocking him is all well and good (and it's helpful), but if you continue to pine away and sit and stew about him, you're not allowing yourself to move forward.
Which you should.
You claim you always knew it was temporary, but you never seem to have devised any sort of an endgame.
We are living in really wacky times right now, and life can feel like it's on hold. I get it if you don't want to spend this time reconnecting with your husband. But at least reconnect with yourself. And do some hard calculations.
Can you survive on your own, if you have to?
I don't mean move in with your kids. I mean get an apartment, pay your rent, make sure you buy healthy groceries and all that jazz. If you can't, then at least put together some life skills in case you have to. And that's not necessarily in this context. Everyone needs to know how to live on their own. The time may come when you are widowed, so you'd have to do something like this then, anyway.
And maybe talk to a counselor (you can get a telehealth appointment these days). Talk about your marriage, and about what was so thrilling about this affair. Get some tools to mentally handle the next few months or so, so you can engage in forward motion.