It sounds to me like you have good reason to be concerned. Paranoia is defined as "irrational fear," and I think your concerns are perfectly RATIONAL.
Unfortunately, if your wife IS back in contact with her (and I think the FB thing pretty much confirms that he is), he's only going to lie to you about it. And asking OW is similarly fruitless -- she will lie to you as well.
As part of your reconciliation, did you and your husband agree to be transparent with each other?
