How do I know if i’m asexual?

I am extremely confused. I don’t know anymore if it’s just nerves or if I truly am asexual. I get turned on a lot by my own fantasies in my head with guys, but I have no motivation to actually do anything in person. Idk what’s wrong with me. :( I’ve never really been turned on by a guy in real life. I get butterflies sometimes.

BTW, i’ve only had sex once and felt nothing.