How do I know he likes me?

There is a possibility of him liking you. The problem is, he's a flirt, so you never know. You won't know until you have conversations with him that don't involve gum, if you know what I mean. Try talking to him about other stuff. Find out what you two might have in common and let things go from there. He'll eventually let you know if he sees you the way he sees the other girls he flirts with, or if you are someone he really likes.