Sadly I don't think anyone here can answer your question definitively. Each situation is different.
With that said, it sounds as if your husband's affair on an emotional level has gone underground and the two are still very chemically connected to each other.
You need to ensure no contact.
Has he sent a no contact letter that you have approved?
If not, he must do so.
Also, ask him to take a polygraph to determined if it's an emotional or physical affair at this point.
Shirly Glass, in not just friends talks about having a detective fund, so you can check on him.
You are not being a fool. It seems as if you caught him with his hand in the cookie jar.
You can't have a true chance at reconciliation until he goes no contact with the OW.
Edited to add: Also if the OW is married please tell her husband, that alone may ensure no more contact.