So you want to know if he's flirting with you? why not ask him?
Work place romance can be problem. I'd avoid it if you can. If things go bad, you still work together and it can be awkward. So, especially since you aren't really interested, just be polite and friendly but keep your distance.
Oh, he's interested in something, it's just figuring out if all he wants is a booty call that is the problem. You could test this by having your mother drop by and introducing him to her. A guy with decent intentions would be interested in meeting your family. A guy who just wants some sex would not.