What I'm suspecting is a deep emotional attachment -- a strong EA. To most women, that's even worse than a one-night-stand PA, but that's for you to decide. My point is that he may be using some self-drawn moral line to define whether or not he's "had an affair." If they didn't have INT together, but have exchanged passionate "ILYs" and "I'm not the same without you" e-mails, then I'm sorry, that's an emotional affair.
Have you read the book "NOT Just Friends," by Glass? It's the definitive work on EAs. Maybe your husband needs to read it as well.
