He's your possessive friend. When you're with someone else, be it a boy or a girl, he won't like it. He just wants you to be with him always, no matter what.

Until you feel his possessiveness is getting unreasonable. He will try to keep someone close to you away, even to the point of being violent towards someone who tries to get close to You.

"Stop acting like that, you know I don't like it, and will do anything." He said seriously and firmly. As if his words couldn't be denied.