I dislike the fact that my best friend hangs out with and is close to my ex-boyfriend
Well I am curious as to how bad you feel since your best friend is always with your ex?
I am super jealous and I want to be with him 24/7
I'm sorry you feel betrayed and want your best friend to yourself, and that's normal. Your ex is someone you no longer want to be with, and your friend is only bringing up bad memories by hanging around them. You have to tell them how it makes you feel and maybe they'll back off.
Talking to them may not be a bad idea, but you are an idiot for suggesting it. Either way, my friend definitely needs to be dealt with.
That's not a nice thing to say to me and you know it, you also know that I'm right. You need to talk this out or else you'll always feel like crap because your best friend hangs out with your ex-boyfriend.