For a couple weeks I've been flirting wi...

For a couple weeks I've been flirting with this single guy at work. The flirting has been mutual and not friendly-flirting, but more my-loins-are-hot-for-yo u flirting. It's a bit awkward at times and he's blushed occasionally. When I inquire about his lovelife, he says there's nothing going on, but later drops that he's dating some girl. Come to find out through a male friend, he's had a girlfriend for over a year. What's up with that? Why the quasi-withholding of information from me? I can't figure out what this guy thinks he wants.