why would this girl I haven’t spoken to in years finally message me back just tell me she has a boyfriend now why is she tell me this?

She contacted you just to tell you that??? Doubt it. That is very strange. I can't see any motive except to try to make you jealous maybe. I don't get it. If you haven't corresponded with her since high school, this is really weird behavior. I don't know if she's playing games or not but I'm not sure I would trust her. That's just a weird way if she's trying to get back with you somehow. People shouldn't play games. I find it hard to believe that she reached out to you after all these years just to tell you she has a boyfriend. No. That can't be her motive. Why don't you just ask her why?