How to talk to a girl you haven't spoken to in years?

Okay so I dated this girl four years ago when we were freshmen in high school. We went to different high schools. We were never really boyfriend and girlfriend but we were the closest thing to it. We dated for a few months and everything was great until she ended things because she said she wanted to meet new people. Although we had only been dating for a few months, I was completely heartbroken and I was never really the same person ever again. I dated a few girls after she ended things with me but I could never get her off my mind. I even dated a girl for a whole year and I still thought about her almost everyday. She dated one guy after we broke up and that lasted all through high school until they broke up recently a few months ago. I recently added her on Facebook again after deleting her off my friends list. I deleted her to see if I could get over her (never happened). I can't stop thinking about her and I really want to talk to her. The only form of communication I can have with her is through Facebook. She now goes to college about 4 hours away from my college so I can't talk to her in person (I would if I could). Please someone help me. I don't want to message her on FB sounding like a total creep because I am not.

Some things I know:
Her older sister and some of her best friends from high school go to my university (I haven't spoken to them since the break up)
Summer is coming soon so we might be in the same city in a few weeks.