Why Do I Feel Like This? Well Written Answers Please..i Will Answer Your Questions Too.?

There’s a guy i fancy whom i see around campus at University, i think he’s really attractive and get a little nervous when he’s near!..
I saw him yesterday after the Uni teaching practice break after a while. He was going into the mail office where i know an attractive girl works there and i got jealous and really angry. This sounds really childish but i went off on one and i can’t stop analysing these little things!!
I also saw him in the morning, got excited it was my chance to make eye contact and say hello but he seemed to freeze and just stood by the bin man!!argh.