Assuming you both survive the initial discussion, it may be helpful to involve your husband in setting some baseline rules. This may help give him a sense of participation/safety. You may also want to give him plenty of reassurance (emotional and physical) during the “transition phase” so that he feels there’s an upside for him. But all in all it’s an extremely delicate and difficult challenge with no guarantees that the situation can unfold in a constructive manner. On the other hand, I’ve known situations in which a formerly very traditional person slowly became more adventurous & open minded as a result of such a conversation. Good luck!