Okay, a few thoughts PB Girl.
I understand why you had a meltdown when you heard that your H had bothered to check if the OW was okay, but you might remember me saying on another thread that it was a respondent on my very first thread (5-6 months after discovery) who gave me a different perspective on why my H was trying to end the relationship with OW, without cruelty. That poster commented that my H's actions after discovery demonstated that this was a man who cared very much and who was taking responsibility for his own part in the affair.
The fact that he had been trying to end their relationship with the least amount of negative feeling, further demonstrated that he wasn't trying to evade his own responsibility for what had happened, or to put the blame on to her. He did care about her feelings and didn't want to hurt her, or be cruel.
Now at the moment, you might think you would have preferred cruelty and contempt for the OW by your H, but a few months on, you might see this differently. He was as much responsible as her for this relationship and at least part of his checking that she was okay, was to ensure that no lasting hurt or damage had been caused to her. These are the actions of a caring man who wanted to take responsibility.
Now that's the primary reason, I suspect, but what you might also want to explore with your H is whether there were subconscious, darker motivations for this "kindness" - keeping the OW "on side" and on the back-burner if he should change his mind. And whether, whenever this "are you okay?" message was sent, he wasn't yet ready to give up contact completely, or to banish her from his life forever.
It took my H a whole year after discovery to acknowledge that if this relationship had ended "pleasantly" and had gone undiscovered, had she contacted him again after a break of some sort, when the bad memories of the rubbish sex, the deceit and the guilt had faded, it may well have started up again in some form. So in his case, at least some of the subconscious motivation for being kind, was a resistance to burning his boats completely with her. He still says he thinks he would never have started this again with her, but he admits that he cannot be certain, especially if this had gone undetected and he had never had to face the consequences with me.
I completely understand your desire to put the OW straight and if this now brings you some comfort, that is all for the good, but just be careful that you don't direct more blame in her direction, than this merits. She is blameworthy, but not more so than your H. He should have said "no thanks" and his antennae needs to be much sharper, if a casual acquaintance tries to strike up a relationship with him again.
The very best way of bringing you some peace of mind as far as the OW is concerned, is if your H speaks to her and is honest, taking full responsibility for his own actions. I understand your concerns that he might meet up with her again through work, but rather than avoid this, I'd counsel you to want that meeting to take place. If your H is able to conclude this and leave no room for doubt with her - and finds that he can be in this woman's presence without it being a threat, that is surely better than avoiding her. Having read what he's got to say, I've got great faith in him that he would do the right thing - so should you.
When I read your H's words, I found myself nodding away, because they resonated so strongly with what my H says about the start of his relationship with OW. Your H seems to be in the same frame of mind as my H was, after discovery. It was clear before he wrote, that he loves you deeply - and further reinforces that affairs happen in happy marriages to people who love their partners very much. But this is why I have said throughout that the vulnerability was with your H; not you or the marriage. Your H is wearing a hair-shirt now and is self-flagellating, while you will want to punish him and see his sorrow.
All this is understandable at this stage, but at some point, he will need to take that hair shirt off, because it can get in the way of proper understanding and unlocking why this really happened.
There is a period after an affair, when the betrayed person feels like their life is ruined, whether they stay with their spouse or not. This doesn't make rational sense to anyone who hasn't been through it and no doubt there will be some lurkers reading this thread who are thinking "FFS, this wasn't even an affair!!" Others will be thinking that a woman with high esteem wouldn't be totally floored by something like this and that your happiness shouldn't be defined by your marriage. Some (as you discovered on your original thread) will believe that no second chances should be given, once emotional fidelity is compromised.
There will be other posters though, who have gone through this, who can truly empathise. I can tell you that you will get past those feelings and get to the point where you will realise your life isn't ruined at all. There may even come a time when you can look back on this as a blessing - a true blessing.
My H often says he wouldn't want to be the man he was in 2008, but strangely enough, I wouldn't want to be the woman I was then, either. I have learned so much, about myself and about relationships, since that time. All this has helped me to re-frame what makes me happy - to value the people who enhance my life - and to devote less energy to the people and things that don't.
Our marriage was good and happy before my H's affair, but it is better now, because there is proper honesty between us.
In 2008, I thought my H loved me more than I loved him - and he thought the same, although he says it wasn't ever something he faced up to, he just sort of "knew it". That's not the case now, we both know that we love eachother deeply and in equal measure.
So make this count for something, both of you. Question everything and treat it as an opportunity and not the dark threat it appeared to be.