I can not speak as a divorced person and certainly have not been legally or otherwise for anywhere near as long as you.
What I CAN say is that my Aunt and her ex D'd many years ago. I'm going out on a limb here and saying at LEAST 15 years. It took my Aunt a long time to get over things (H left her for OW based on historical data) and the D was horrible.
The short story is, after much good advice she received over time (similar to what is offered by DB), her and her ex are now friendly.
I don't think they would ever get back together, she still calls him stupid (and I'm sure he still calls her crazy), but they are actually quite friendly and sit together and talk when I've ever seen them together. They have two children and three grand children. AFAIK, he is still with (an) OW (if they can be called that, now; she remained single this whole time) and (as described) neither have remarried.
So I think what I'm observing from some that I know quite well of long term D that have "re-connected" (and this is pretty much what we would advise here, no matter what) is that unless BOTH parties indicate there is interest to re-build the R, then all you can do is just be civil and treat him at least like an acquaintance and at best as a friend, depending on how much he leans towards you and is open and honest with you.
If, as you say, there are emotions that are creeping in that you'd rather not deal with, then be as distant as necessary for your own well being.
I wish you well.
For the record, I would say it really is a shame that your H stated that he left because of your oldest and lack of sex... I hope you have let that one go. Those are his issues that he will have to deal with if he hasn't, yet.
