Hello... I would have to say that I your past relationship experiences have most likely made you more sensitive to relationships your partner is having. That being said it is hard to tell if his relationship with "Sally" has crossed a line. It does appear to possibly be heading in that direction by your description if it has not already gone there. Although at this point I think is unlikely that he sees it as anything other than sharing a common passion with someone. He does not seem to be hiding anything from you which I would say is a good sign.

I think the big win here is that he is making an effort though counseling! I hope though counseling you two will be able to understand how this other relationship is effecting your own, open up and communicate effectively. Communication is key.

I wish you well and hope everything works out. I think you are on the right path.