I would sit down with him and discuss why he or she as become so possessive.

Maybe your friend feels insecure. I would just say that you need to have lots of friends so that you can share in many ideas and different points of view. If your friend becomes so possessive that you can't stand it, it's time to end the friendship.

i was thinking that if your friend is possessive with you, maybe wants to get something more than a friendship with you, because I'm not possessive with my friends

I go along with Norman's answer. You can't go on very long like this.

Hi... yes if your friend becomes too possessive when you talk to someone else it is a lack of confidence ... So you need to reassure your friend, each time... If you are not ready to do that then your relationship will not be successful...