Doesn't sound to me as though the husband wants to get involved with the activities and such, as others are suggesting he do. Then don't do it! Lay around in the sun on the ship and have the servers bring drinks all day while you listen to the music. There is an arcade area on board where he can play the video arcade games if he wants. Eat in the buffet area and don't dress for dinner. Or order room service and play games on the laptop.
It was hard as h3ll getting my brother-in-law to go on the first one. He was the same way. But once he was onboard and sitting in the lounge drinking a beer and watching the ship sail away he was like......................"cool!"