Kboys-
I don't know what to suggest, I just want you to know that I have a very similar situation.......and have had the same rainbow or reactions that you have. Really, truly, including not too long ago a VERY LOUD "Good Morning," to acknowledge that I had seen her in the grocery store, saw her recognize me and then not be clear what to do in the check out line.
It is not mature by any stretch for me. She was a good friend at one point (I have not run into my ex in the same way so I am not sure what I would do, but I suspect it would be similar).
I think MY reaction is somehow me trying to define that "I EXIST, I MATTER AND I TAKE UP SPACE IN THE WORLD." Even when my hubby's behaviour in the affair undermined that belief in me.
Though this part has changed over time I still have a physical emotional reaction when I see either of them.....even from a distance.
Thanks for posting....it makes me feel less alone, and reminds me that though I am not proud of my behavior....it is in the range of "normal" considering the absurdity of the situation.