LOL Sorry to laugh at your situation. I'm laughing because my wife and I have had the "slow down" talk....RECENTLY! LOL And it is defniatly just NRE.
Your hubby is excited because he is recieving attention from another woman. (I was/am there also) It is such a high that I can only compare to cocaine. It is such a hihg that a person will do almost ANYHING to keep it going on. The fleting glance...The secret wink....a little kiss blown to you. It's captivating.
My wife was such a trooper, because she was in your shoes just a little over a week ago. She told me to slow down.....I did for a day...Then kicked it into overdrive. I got in trouble QUICK. I never crossed any PHYSICAL lines, as in touching or sneaking off somewhere, or anything. But....I thought I was in love all over again. My wife stood by and allowed me to handle my NRE the only way I knew how.....With the other woman. D (the other woman) and I met in public, and talked about it. We agreed that it was best to slow down, and at least TRY to not act out. We also agreed that it was simply NRE, and not "love" yet. In fact, we both agreed that we would likely never "love" each other the way we love our spouses. And since neither of us is leaving our spouses, we would have to continue to be FWB. Or Friends With Benifits. It works for everyone involved for now.
Now, I will say in hindsite, the best way would have been to sit down and talk with EVERYONE involved. So, you, your hubby, and C need to sit down and discuss your relationship dynamic and how it should progress. Discuss your concerns. I'm pretty sure that C does not want to make you mad, sad, or anything negative. And I'm 99% positive that your husband doesn't either. In fact, I would venture to say that no-one in your relationship dynamic wants to make anyone else in it anything other than happy. So sit down and have a nice chat. Get everyone on the same page....Then have a nice little make out session.