How to prove to a girl that I am ONLY acting jealous because we are not in a relationship?

CLOSE FRIENDS - Me and this girl had a talk a few days ago, and overall she said that she likes me BUT she finds me extremely jealous person - said that I lose my mood when she talks to other guys, friends and such, on which I think most of it is bulls*it and past experience/past relationship issues from her relationships.

The truth is - yes, I am jealous when she talks to other guys ( that are not her friends and I see that these guys are hitting on her in my presence) but I cannot agree that I am being jealous that she talks to her friends or whatsoever. Also, since we are not in a relationship, I cannot say ANYTHING to these guys or act in another way, as again, we are not in a relationship and she is a free person regarding that topic.

Cause... there is a significant difference between going out with her in a group like JUST FRIENDS and not being able to stood up if another guy approaches VS actually being together and setting clear barrier that she is only talking with them in a friendly way.

My question to you - how can I assure this girl that my issue is only seen in the pre-relationship phase and that she won't see any of that jealousy level IF WE GET TOGETHER?