In my own humble opinion, I don’t think this is a wise question to ask yourself. For one thing, you don’t know what it means to “fall for” someone, so you’re asking us to define “how you should feel” if you’re in love. What kind of secondhand nonsense is that?
You might get better responses from yourself, even without asking a single person anything, if you can answer (to yourself) “How do I feel when I am around this person?” “Do I like these feelings?” “Does this person seem to feel the same way?”
And those are good questions for you to be able to answer, but that’s still not all of it. Because you’ll want to test whether the person that you believe you see is the person who is really there. So you need to investigate whether the person acts differently toward you (or when in your presence) then toward others, or when not in your presence. (This is going to be difficult, because if the person knows that you’re observing him then that can influence his behavior. But spying on the person without his knowledge is going to make you feel bad about yourself, too.)
So it’s a very careful process of observation and analysis of your own feelings that matters, not what someone else says is your outward manifestation of whether you have “fallen for” someone or not, or your attempt to reconcile your feelings with what others say you should be feeling.
You should definitely analyze this, but your feelings are part of the analysis, so you should analyze them, too.