OK, your dog is adorable, but remember he is a dog, and as a dog he believes that there should be a leader in your pack. And apparently it is him. Is he neutered? That may help, or not. Either way you should (need to) step up to your pup and , no matter how much it may hurt you, teach him who's boss. Surprise!!! It's YOU! He is pretty young and you can still instill in him your dominance, if you don't feel you can do this then goodluck just having your furbaby as a partner, I don't think anyone would want to put up with a dog that growls at them.
I have seen many instances where a dog won't even let their "owner" mother near them. That, my dear is WRONGO. Don't be a victim to that adorable face ( we all have been at one point
) you should be proud of your dog and eventhough training may be hard it is worth it when you receive compliments on how "well mannered" your little dog is. Trust me I know
Good luck !