How do I know if he's interested?

There is a really attractive guy that sits behind me in cl. We've exchanged flirtacious witty banter. But he is very attractive and me not so much. I asked him to tag along with me to go see a movie with a couple of other people in the cl. He said yes and gave me his number so I gave him mine, But I don't konw if he's really interested or he's just being nice.