He wants to watch... while I have sex with another guy

Dear Diana,
I'm 27, married for the last five years. I have a two-year-old son. My sex life with my husband is also going fine. One day, my husband had a strange idea to introduce a second man during sex. I feel it's a perverse idea and told him it could ruin our relationship, but he insisted on a threesome as he told me it was a one-off. He introduced a man as his friend for it. To my surprise, my husband was a mere spectator while the friend and I had sex. Later on, he told me that he enjoys watching me having sex with another man. I was shattered and now he insists on always doing this. Does my husband need to visit a psychiatrist ASAP. Otherwise, our sex life is quite okay.