How would you actually know if you feel romantic attraction?

So first of all, I am male (if that is relevant) and approximately 16 years old and I am very likely autistic. (I don't have a diagnosis, but I am currently waiting for a place for diagnostic procedures and my therapist is very certain that i have ASD)

I don't understand how you would differenciate between romantic attraction and other forms of attraction. I don't really understand how to differenciate between different types of attraction at all. I know I like someone, because I eg. like spending time with them or because I like being around them.

a specific example: i have a friend (she is female and 15 years old). We do activities that are stereotypically platonic (like playing video games) but also activities that are stereotypically romantic, like going for a walk together or sitting at a stream together.
As far as I know, her mother thinks we are secretly in a romantic relationship, and some of her friends do that too. I try to keep her existence in my live secret to my family, because whenever I had female friends before, my family acted really weird because of that.
I don't think she likes me romantically, because she says she doesn't. But I am aware that many people would say the same thing if that wasn't true. Another close friend of both of us once told me that we give off "romantic vibes", but when I asked her to specify what those vibes are, or what makes her see those vibes, she said she doesn't know.
How would I know if i like the friend romantically? How would I even know if i like people romantically at all? How do alloromantic people know they like someone romantically?

Sorry if the text is a little chaotic. If you have questions feel free to ask them.