Actually this doesn't mean someone won't love sex.
I was someone who waited until I was 23 to have sex but I am a very high libido woman. I want to have sex every day. And before I had sex with my partner, I would masturbate multiple times a day, every day, since I was about 12.

I just am demisexual so I need to feel emotionally connected before I want to have sex with someone.

And unlike your theory of monotogamy I STILL have a high sex drive, 6 years into my relationship. In fact it's higher than my partner's.

Someone being choosy about who they have sex with but still having a high sex drive is not impossible.