Yeah I was gonna say that. He was famously single his entire life and is speculated to be one of the first historical examples of an asexual and aromantic person.
They're not fictional, they're mythical. Here's the difference between reality, fiction, and myth: Fiction is made out of the rearranged parts of reality. Myth is made out of fiction that people thought was important. And reality is made out of myth that people took too literally.
The Greeks didn't understand asexuality and thought it was hubris, since the only examples of ace people they did accept were literal gods. Narcissus was 16 when he died. A 16 year old who constantly gets sexually harassed has the right to be a little rude in rejecting people. Ameinias, for example, asked for the 16 year old's hand in marriage multiple times. If you want to say hounding a mid-pubescent child for sex is acceptable in any cultural context, then I'm going to view you the same way I view the ancient Greeks: as a pedophile.
Narcissus literally loved no one above himself. It wasn't asexuality it was hubris in the form of solipsism and narcissism - the reason why the condition is literally named after him.
And the Greeks cerainly DID understand asexuality, go and read Hippolytus.