Won't make it fb official?

So my bf and I have been together for 6 months, he calls me
​His girlfriend, but won't make it fb official and never post pictures of us together... I've talked to him about it several times and he always says he doesn't want people knowing his business, am I over reacting? I know this isn't some highschool relationship but I still would like for all of his flirty friends that are girls to know he is taken.