Guy's Behavior

Why would he act so uncomfortable around me?

There’s this guy I worked with and I found him to be attractive. Not overly attractive but I was attracted to him. It wasn’t burgeoning or anything but I did notice him.
We also go to the same college and one of our first conversations involved us talking about pizza because it’s my favorite food. He asked what was a good pizza place for him to go to and the next day I asked him if he got his pizza. And he smiled and said he did.
He also said I would be a good reporter because I speak very eloquently. I was dating someone and he knew and we were talking about food and he asked where me and my boyfriend went to eat.
Before he was talking to another coworker from our job ( she doesn’t work there anymore ) but I doubt they’re still talking.
He would help me when I needed it and would talk to me sometimes without any problem but I later started to notice that he would not make eye contact with me anymore lol. I know I’m not hard to look at I actually get called pretty a lot but I don't know I just assumed maybe he was nervous or something.
A few weeks ago I went up to him and asked him was he burning up in his jacket because it was hot in the store. I guess after that point he took it to start a convo with me and told me he would be graduating that next week. I congratulated him and then he started talking to me more about his major and stuff and wouldn’t look me in the eye and started stuttering really bad lol.
It was pretty awkward. He’s not shy, I’ve seen him talk to other people just fine but he is very laid back.
Why does he seem so uncomfortable around me all of a sudden?
Why would he act so uncomfortable around me?
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