Oh, I admire that you have real crushes but can see how they'd be problems when you run into them; I had a made up, imaginary one at your age so I couldn't run into him ("Michael") but yours aren't that far removed.

Make some friends, talk to people sitting next to you in class, raise your hand and ask questions of the professor and then get braver and answer questions they ask. Start allowing yourself to be seen a little bit so it's not so hard to approach you. What people don't know about us because we don't engage with them, they take to be stand offish, cold, and other things we're not! Conquer your fear of being rejected. Your self esteem can't grow if you don't "exercise" it by putting it to the test and talking to people and getting real feedback instead of imagined.