OK- maybe they did cross the line, but there's no way I will ever believe it was anything more than scratching an itch with the safest person around.
Well, ntf, this is supposedly how it started out. Teri wanted to get back at Jon for having affairs, and decided she'd go after a friend of Jon's. Dean heard about it and offered himself up for the sacrifice. [Yea, big sacrifice
If you go back to the Nfanfic boards and read up on the original George and Lynn story you can see how this played out. Really great nfanfic!
Whether or not it's true, I don't know. I just know there were a lot of indications that it was.
*Disclaimer: This post is based on things I have heard and read, but have no idea whether they are true. It's my opinion, only.*