....A few things about us guys to keep in mind. One, we often act without thinking; think we want something that we later realize we don't really want or we regret later ... ie. like a new boat or car. And two, we often confuse our realities with our fantasies, and we do often have fragile egos.
....So, you definitely want this to happen because HE wants it to happen. You might mention the idea of having a 3-some to see where that takes you. Maybe watch some interracial vids together. But, he definitely needs to 'lead' on this one as he won't easily forget what has happened after it happens, if he's regretful. This 'fun' is not worth damaging a marriage over, that's for sure.
....Good luck ... Mac