How can I stop being a jealous boyfriend?

I’m not a super jealous guy, I don’t tell my girlfriend what to do and what not to do. For example, guys like to flirt with her and she was telling me that some guy has a crush on her at university (that she already established she didn’t like and thought was nerdy).
I compare my situation(s) to other people, and they say that mine is nothing compared to others, I just feel that I don’t need to be this “inner jealous”.
Any ideas on how I can get over this?