Most Helpful Guy
I don’t usually recommend giving an ultimatum to a relationship partner. However, in this case I think it would be appropriate. You tell him that he needs to openly acknowledge the relationship or it will be over. If he can’t do that, I would be wondering if he is doing something shady.
Most Helpful Girl
If he doesn't care about your feelings and you are old enough either you start telling people yourself or let him go and no one is the wiser.