What do i do? what do i say?

Right I broke up with my ex girlfriend over a month ago, long story... won't be taking her back unless she got on her knees and said sorry from the bottom of her emotionless heart.. right anyway, I was in work on Saturday and ex-exgirlfriend walks into the bar, I didn't speak to her, my mate did.. he didn't realise who it was until I said, and then he was bouncing about the saying how pretty she was and so on.. before she left (wasn't there longer than 10 minutes) she stood at the end of a busy bar waiting for me to notice her, in the end I did say alright, and she waved smiled and hi. I then went on Facebook to find "Hey, look i know what happend yonks agoo, i wish we could be friends again? I know i shouldnt have done what i done, but please can you forgive me ? Please reply back even if it negative :( jess" I have yet to reply as I have no idea what to say, and when we were together she was celibate, I don't mean to sound nasty or anything but I'm an 18 year old boy! I can't be dealing with that, I know I sound bad but I mean perhaps she just wants to be "friends" help anyone? What do I say to her?