Ex Girlfriend Issues

So I was flying home after visiting my aunt and I sat next to this girl on the flight and she was going to be starting at my university in the fall. We were talking and she told me she was moving out East because her ex boyfriend lived there are she wanted to work things out with him and get back together (they're still friends). The only problem was that he has a girlfriend but she might be leaving for vet school across the country in the fall. At this point I'm feeling sick to my stomach and I ask her ex's name (it's a small university). And well like I'm in a movie I relalise this girl is my boyfriend's ex and I'm the girl she's trying to take him from. I didn't say anything else (we were getting off) because I was just so stunned and all I could feel was panic. 
Anyways I'm seeing my boyfriend tonight and I have no idea how to approach this. I know I need to talk to him about her but I'm so worried he knew she was coming (I am aware he still talks to her but they've been friends for a long time). Should I tell him I know about her plan for me/him? And how the hell do I get that out without sounding crazy?!