DAE have trouble telling if they're crushing on someone romantically or platonically?

Okay so like, I have a crush. And I can't tell if it's just because I think he's really cool and I want to be friends or if I am attracted to him. I guess both can be true. But then I get SO SHY and don't know how to proceed because I don't know what I'm feeling. Does anyone else get this? How do you approach making friends with someone new that you find interesting?

This specific situation: he followed me on insta and sparked up a conversation. Then we ran into each other at our climbing gym (where he works and I'm pretty well known). We spoke and we're both doing PhDs but he just submitted. So then I messaged him to wish him luck at his defense. He never responded but when he saw me in the gym today he came over and started up a conversation. But I got shy and left even though I wanted to talk to him more. And it's because I don't know how to approach the situation regardless of what kind of crush it is.

How does anybody else deal with this? How do you tell the difference between platonic and attraction?