I get nervous

I'm usually an outgoing person and can talk to anyone... but when it comes to this guy I get super nervous. We had a "thing" freshmen year of college, it was nothing big.. we just got along really well and we both had feelings for eachother but nothing happened. I didn't think I would see him again but he's back and we have a class together. I didn't want to talk to him but he came to me & then I started getting nervous and I actually got kind of sick LOL. Now every time I see him my heart starts pounding and I just can't seem to verbalize, I feel so silly lol.