Why does this guy act like this?

When I'm around this one guy he acts all shy and quite. He use to be really outgoing and talkative around me. and he still is with everyone else except me. My one friend noticed that he is always looking at me. Also when I stopped by to see a few of my friends before their show they were doing he saw me and he came up to me acting really nervous and he had his arm out like he wanted to hug me and he told me I looked really pretty. a few people told me that while he was walking up to me he was fidgeting with his fingers. When I talk to him he'll stay very quite or laugh or he'll talk and kinda stutter. I am starting to get a little paranoid because like I said he was outgoing one day and then shy the next!