20 years ago I was in a similar situation at OP's exact age (Im old, yes...but married and stuff, so I managed to move on, as will everyone).
Was in this weird friend zone, but there was some tension...it was really f'd up, totally still think we both were too scared to lose the friendship (which still exists, but like any 40 year old, we rarely cross paths due to normal lives - and when we do its clear we both turned out just fine with other people). I actually was gonna tell her...like I knew she was home on a certain day, and I actually called out of work sick, and was gonna see if she wanted to hang out like a normal thing, maybe hit some tennis balls, as we'd do now and then, and I'd take my shot, and let her know, probably in a god awful clumsy way...and I was freaking out..and I called her..AND SHE WASN"T HOME...I made the freaking call!! I was gonna do this!..that night, we met in our usual group of friends at our usual happy hour spot...and she brought some new guy along (who turned out to be an asshole eventually)..I got REAL DRUNK that night.
So what am I saying...I dunno...for a long time I wish I told her..but I never did..but a lifetime later it really didn't matter - there are A LOT of people in your future when you are 21.