Why was I shaking this time?

So, I went to dinner with this guy I consider my best friend. We talk all the time. I have been with him on dates before, but this time I couldn't stop shaking. It was a little chilly, but not enough to usually make me shiver. I don't know what it is that made me shake this time. He is a great guy. I love him, but I don't think I would ever date him.