I have similar problem. Tho im not asexual for sure, I have large problem with the "erotic" part of the relationships. I just have this aversion to it.
I have probably developed it in the childhood where I was quiet kid for the most part. But when the puberty striked, suddently I have become more attractive to girls who hitted on me like crazy. But there was a problem - my body might have been ready, but mind definetly wasnt. Popular girls even touched me around just to flex on their friends. It was unconfortable as fuck for me. Eventualy tho, I got more bold and started going out with those girls on the night outs. At first, they were great, but when girls realised they could not experiment with spicy stuff with unexperienced quiet boy like me, they just have gone to older men and I have just became their "sidekick". That completely destroyed my perception and trust in women. And considering I was 14, all that shit stuck with me (there was also a cases of public harrasment by one female teacher but idk if I want to talk about it).
Nowadays, I know there are a lot of great women. I dont even have problem flirting with them. But when shit gets real, I often become nervous, or when I feel confident at the time, I just get repulsed by it.