Girlfriend had a severe jealous hissy fit?

I totally understand what you mean. Your gf shouldn't be getting so angry about your friend. I have a best friend of the opposite , too. We've been friends for 4 years, and we just have great conversation with each other. What you said to your gf was very polite, but to the point. She's going to have to realize that you're going to hang out with your friend no matter what, and she can either get over it, or not acknowledge it at all. Her choice.