I think that you're just being influenced by the general tendency when you try to check on your crush on different networks. The same about posting your question on different forums. I'm sure every generation had its own tendencies and this particular one that so many young and old people are responding to nowadays has become somehow acceptable and not a very worrying thing unless it extends over long periods of time, IMO.
He might not be the real guy for you if you feel that you don't have a chance in real life and he has a girlfriend, plus she blocked you on twitter when you sent her a friend invite, but you also said that there are other people from campus that follow him on instagram, so it wouldn't be very unusual for you to do it too, unless you have already exposed your crush to him in other posible ways and he rejected you.
I think that having a crush on guy you shouldn't it happens pretty often but don't ever make a fool of yourself and be smart enough to recognize when you should give up and start looking around because there are other interesting guys that may be available and interested in you.