I think you and him need to have a conversation or two. Why does he want this to happen? What’s his fantasy here is he gonna be able to handle it if it became a reality. Are you truly OK with doing it or what do you get from it? I had met a husband and wife couple. He wanted to try it. Bisexual threesome with another guy. After lots of discussion, we decided we would go for it. For me it was not the first time, but for either of them it was a first time for a threesome and his first bisexual experience.
To make a long story short once the sex started he chickened out, but his wife didn’t wanna stop. She rode me well he sat in the corner pissed off For me. It was very awkward and uncomfortable with a whole lot of guilt for not putting my foot down and telling her to stop. It was also pretty clear that really damage the relationship. Now I had done the same thing with two other couples at all those experiences were amazing. So as long as everybody’s willing and there are clear-cut boundaries, it could be a lot of fun.