How do I get out of this awkward situation involving Facebook?

[Lauren the Football Princess]

My old Supervisor, that used to be at my workplace, is now trying to chat with me on Facebook. He added me a few weeks ago. There really isn`t a purpose to adding me, other than to probably start something up or flirt with me.

However, he has a girlfriend of two years, that he lives with. I`m not the type of person, that would ever get in the middle of someone`s relationship on purpose, I think it`s wrong, and I wasn`t raised to act that way. Things such as Are you working tonight? Did you miss me? Stuff like that. He was a big player, back in the day, and would always have some new girl, he was hanging around. I want to be polite, because I work with him, but it`s so awkward, because he keeps messaging me, and it`s really annoying. He always got attention up at work, and all the girls had a crush on him, but I see beyond that, and I just don`t even know what to do about it.

He`s in with other people I`m friends with on Facebook. Any help, or advice, is greatly appreciated! I don`t want to tell him he`s being inappropriate either, because what if this is all in my head, or I`m imagining it. So, again, any help?
BTW, I put this question here, to possibly get more answers.
@ Stuffed Rabbit, I tried to Facebook friend her, but she won`t add me back! I tried to do it, so it would be less awkward. This was weeks ago, she still won`t add me.

[Stuffed Rabbit]

Message his GF, let her know what he's up to.

[Faith]

just don't answer him , when he asks why you aren't answering him don't answer him about that either. If you really want nothing to do with him then let him know and he'll just have to deal with it . Don't let his girlfriend know because it's not like he's been asking you out or saying sexual things to you . Good luck

[dan]

" or flirt with me " ???????

Young lady 99% of single male users would love to flirt with such a pretty girl as you.

[TVoth]

You can hide yourself from him on facebook chat so he would never know when you are on. If he messages you, just simply ignore it. Basically don't take anything he says to heart and ignore him as much as possible.