I have just now had a chance to read your thread. IMPO, adding a 3rd person to the equation spells nothing but trouble.
In some ways I can understand the "fantasy" of this, and the fantasy is not uncommon. Doing this in reality however becomes complicated and often ends up in hurt feelings, resentment, jealousy, affairs, and divorce. I simply would not go there.
I may have missed this since when I had a chance to catch up on this there were already 60 posts...but does your H have someone in mind? If so, I'd investigate that a bit. Definitely talk about this in the C's office. It may be as simple as a fantasy your H thinks would be fun to fulfill, but there may be underlying unfulfilled needs that he has too that need to be addressed....and he thinks adding "spice" this way will do it. Personally, I doubt it would.
Perhaps you could add spice in other ways. Try new things you've never tried before, but stay away from involving other people.
As Honeypot has already told you...if this is a problem for you, and something you have to "think" about...the answer is "NO". It really sounds to me like you are feeling pressured to do something you don't want to do...so don't do it. If you feel pressured into it, you will definitely regret it....and it won't fix what your H is going through.
