I think it's definitely possessive. At the very least, it's manipulative and he's revealing his insecurity by sulking about a (most innocuous) remark you made to a friend or you wearing a Pride necklace. From your description, it sounds to me as though he's trying to manipulate you into giving him more attention. He probably doesn't realize he's doing it -- maybe it's an ingrained habit by now -- but manipulative it is.

And there is no rule that states that only ONE person in a relationship can be possessive. Maybe you both are. Either way, it's not a healthy way to function in a relationship.