I can really, really relate to this. Im 20 myself and I am having the exact same experience as yourself.

I've been in college a few years now. Thankfully, ive only found myself in intimate situations with girls on a couple of occasions. I would also be described as reasonably good looking, I lift weights etc. but not many girls approach me. I get lots of looks, but not many approaches. I'm pretty sure its because I never send signals to girls or react to their signals. Perhaps you receive girls flirting too enthusiastically? I know it sounds terrible, but perhaps be a little less open and friendly if that is the case (bad sacrifice to make, but it should work).

As for the friends, well my close friends all know my situation, some are understanding, some just downright take the p*ss. It doesn't bother when they mock me when its just us, but it can be a bit embarrassing in public, which I can usually play off very well, as for whatever reason people that don't know me well, think I pull lots of girls. I don't know why, because I may kiss a girl once or twice a year, and that's just my annual act of intimacy to appear normal.

Goodluck mate. Not to sound too corny, but be true to yourself. Don't cave in to the pressure of others if its not something you want to do.