Is sex life

Been with my husband 6 years. Our relationship has always been wonderful we never fight, never argue. Sex life has always been good, adventurous, non judgmental, and freqent. My husband asked on our anniversary (last monday) what my thoughts were on a open relationship, he stated that he has a strong desire and need for sex, and that even how frequently we have sex (4-9 times a week) isn't enough, and that he feels "starved" for sex.
I do not think that sex makes a relationship, but I do feel it can break one. Not the jelouse type but still
Why such a high desire/need for sex?