Getting over an ex

A few months ago, my first real boyfriend cheated, lied, and broke up with me. I was obviously upset at the time, crying every night for about a week but I finally realised I can do so much better and I got over him. Atleast I thought I did. School started recently and I’ve been seeing him around everyday and I freak out whenever I see him. I get nervous and stressed. Whenever I see him talking to girls I also feel something... jealous, even. I don’t know how to stop feeling this way all I want is to get over him and make sure he knows that. It’s not that I miss him, it’s that I miss the relationship. Because I did love him once... or the old him atleast.