My husband wants to join in with my girlfriend and me

My husband really loves me to be having my girlfriend and I have really hot and very wet sex with each other, but now he is always asking for to join in on our sexual adventures and we are both happy to have his fat cock and his tongue deep inside both of us. But also I really want him to stop asking me if he can join. We are just waiting for him to just do it and give it to us. What do I need to do or say to him? And he is always saying that his cock is to short and to skinny. He has a good 8 to 9 inches and is about as round as a dollar coin. How do I or we convince him that he is just perfect?