He’s probably had too much trauma from Gems to ever be sexually interested.
Not to mention the only one who ever seemed interested in any way in the concept is “gross mom” Amethyst and him knowing she grows a penis to beat up humans. The rest are pretty sexless, either because “in a relationship, leave me alone”, being grossed out on an almost spiritual level by organic things, having a childlike view on the world, or being aware of the pain they are capable of inflicting regarding the closest analogy to sex for Gems.
Seriously, he’s seen Amethyst mindbreak Garnet by mistake into losing their identities together, seen Pearl obsess and lie and almost murder to get into anything that reminds her of Pink, seen Garnet acting in damaging and contradictory ways based on the current disagreement between Sapphire and Ruby, seen what Lapis did both to herself and Jasper, and Steven treats Peridot like she’s Onion’s age. He still dislikes the Diamonds and Spinel to a strong degree, and is paranoid about Aquamarine and the Ruby Squad.
The only remaining candidates are Bismuth, his mother and the Rose Quartzes, the Uncorrupted and Nephrite, and Yellow/Blue Pearl.