What he is experiencing is just plain old jealousy. I had those issues to when we first started. Reading this board helped me work through allot of them.
I was excited as hell about the whole thing, then I'd get jealous, then excited. Finally Mrs. WS just came out and told me to stop it, my insecurity was taking the fun out of it. And that was it. I was insecure. Insecure that I was enough for Mrs. WS, that she'd enjoy sex with others more then me, that she'd leave me... then the idea would turn me on again. It was a real conflict. A conflict that pissed me off about me. I am usually a very self-confident person and this was definitely not me. I started to think about it and what was causing it. It really revolved around my ex-wife and her cheating on me and leaving me for one of the guys she was seeing. The fact was though that Mrs. WS is not my ex.
So I worked through that. I refused to let myself get eaten alive by this dragon. We slowed down to my pace and eventually after more and more positive experiences I became more and more confident and here we are today.
Basically, he needs to get over himself. It's not you. It's his problem and he needs to own it and conquer it. He will be very happy he did.
There are several good thread about jealousy on this board. You can start at
http://www.swingersboard.com/?swing=jealousy . Read them together, or let him do it alone, but seeing how others have overcome it will be a big help.
Mr. WS