Why did he flirt one day, then act so aloof the next?

So I visited a good friend of mine this week. He's been interested in me as more than a friend for a while now. For the first three days or so, he flirted incessantly, from goofy pick-up lines to pulling me close and kissing me on the couch. He's got a lot more experience then I do, so I let him lead, but eventually I worked up the courage to make a move myself. It was when we went to a movie, I lifted the arm rest and snuggled up next to him the way he'd been doing to me. He seemed pretty uninterested though, so eventually we just moved apart again. I was silently offended. However, later on, he was back to flirting again. What's with that?