Ah, so you know about the PA. Well, then, why his sudden issues? I'd say that he promised OW not to cheat on HER, lol. That big guilt is coming from somewhere. Anyway, it is a possibility that YOU are starting to become the interesting one to him in all this mess as the one he is sneaking around with, lol. WTF knows. Really no reason to think about it, but I can make up stories as well as the rest of y'all.
Anyway, with respect to OW and the kids, just tell him that you are concerned about the kids and prefer not to have them introduced to OW until you can let them know together. Also, you might suggest that you check with a professional to see what the best way is to go about it. But, put the responsibility squarely on his shoulders. Because that is where it is. Ultimately, the kids will meet her when HE decides, no matter what he promises you. Here's a thought you might share with him. The kids should NOT be the path to the next level, he should be on that level before he brings the kids into this. Why? For two reasons. First, if he feels as though introducing OW to the kids is that high stakes, then he will lose freedom once he does so to really evaluate where he is and what he wants. He'll feel he has to stay with her (more or less) because he took things that far. Second, it will be difficult and confusing for the kids. They shouldn't have to put up with it UNTIL he is sure that he is invested in seeing it be a LTR or M.
Anyway, that comment from your SO just shows how out of control he is. He sees this stuff as happening to him rather than him running his own life.
Baby girl, July 9. My first, his third. Both second marriages :-) I am so grateful for DBing because now I know what I want from an R and appreciate it so much more. It is a totally different second M than I would have had otherwise, I'm sure. It is what a healthy passionate supportive honest trusting M is supposed to be like.
I will likely not be around much, I hope. I have a HUGE STRESSFUL PROJECT that I am procrastinating on, and it is so much more immediately rewarding to come here and help people... But, I have to buckle down and work like crazy.