Why is he calling me sweetie? Help!?

I've had a great guy friend for years now. We had a thing for each other years ago but due to other cirstances nothing flourished. I'm completely head over heels for the guy and he has a girlfriend he's been courting for about a year or so. When I spoke to him a couple of months ago he called me sweetie on the phone, which I found strange considering he'd never called me that before. I ran into him and his girlfriend also about 3 months ago and I felt like there was still a connection there. He again called me sweetie. Why would he do that? Is this just a friendly pet name? Why would he say that in front of his girlfriend? I really don't like it.