You might be the best your husband has had but not the best his friend has had. Ask him what will happen if his friend is not impressed? Or worse, if his friend is so turned on, you are now the fantasy that his friend masturbates to. Does your husband really want his friends to think of you giving head to them? And if friend wants to join in while watching? There are so many things that can go wrong. Tell your husband you are glad he’s happy, but what goes on in your bedroom is private and you are insulted that he thinks it is a spectator sport. Next he will be asking for a threesome. Shut that down as well.