I am not sure, and the only people who would know would be your ex and this guy. They are probably just flirting, so I wouldn't worry about it.
I don't know how you would get her back, it all depends on this girl. If she truely cares about you like you do her then she will eventually someway somehow try to get back with you, no offense but she did break up with you, and I really think that you should move on... I know it is hard though, I've been there too....
Just think of all the cute girls at your school, and pay attention to the way they talk to you, or if they run up and hug you or get really excited when they see you, those are the girls that MAY like you. It is hard to notice though, alot easier for other people to see.
I don't know what else to say anything in specific you need? Just ask and I will try my best to answer.