Re: If you discovered your H/W is in touch with their ex?.........
First, how did you find out about this communication?
Did your husband tell you, or did you find out on your own by other means?
From what you are describing, it is not seeming healthy.
The best barometer in such situations, is whether there is secrecy or not.
For example, on my father's side of family, there is occasional contact between some of my uncles and their own ex wives, but this is because there are children between them and ex's, and a relatively cordial and mature relationship between their ex's and their family. There is no secrecy in this example, so in such situations I would view as acceptable.
YOur situation however is not seeming as this. Your man has decided to hide his communication, you hinted at a previous EA or PA with this woman, and there is strong resentment (of course) welling up inside you concerning his communication with this woman.
If there is secrecy, it is definity not proper.
Decide what to be, and go be it. -Avett Brothers.