How do I know if a guy is falling for me?

There's this one guy in my class that has been acting suspiciously for the past few weeks. whenever I turn around I catch him staring at me and he starts texting me more than before. well, the thing is that he had a crush on me last year but I ended up rejecting him cause I had no interest in him. he took it way too seriously and he just ended our friendship cause I said no to his feelings. but as I mentioned before, he's been acting a little bit different than usual and the only explanation I can think of right now is that he has feelings for me. what should I do and how can I know the reason behind his behavior?

How do I know if a guy is falling for me?
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