I'm not some dumb teenager why am I like this?

Okay I'm 23 year old legal professional, who was quiet content in my status of single and NOT looking - until a few weeks ago. This guy comes along and in my hazed - post football game - alcohol induced - stupor and I actually start talking to him. We hit it off well and I ended up seeing him again the next night (with no alcohol involved). I am usually very well spoken but for some reason I am so nervous around him. I keep getting tongue tied and and losing track of my thoughts when I'm talking to him. He just makes fun of me for it, but seriously its driving me nuts. Someone please tell me how to calm down!