How long does it take for you to get over your crush?

I've had this ridiculous high school like crush on this guy for a looooong time now. I'm pretty bold in other areas but this guy knocks me off my game and makes me feel super self conscious around him (I can't even look him in the face). Anyway, me and my friend saw him with his brother last weekend and my friend stopped him to say hi. I was getting something out of my car but after my friend stopped talking to him he just stood there for a while and my friend said she saw him look over in my direction. Finally he walked off with his brother. I was sooo nervous I couldn't even say hi, I just kept looking for that stupid cell phone in my car! My friend said that he may have thought I was rude (which I'm not, just extremely nervous). Do you think he thinks I'm stuck up and rude and if so, how can I change that perception that he has of me?

Also, guys, when you're crushin' on a girl, how long does it take for you to get over your crush if you don't interact with her? Thanks! :)