Why Is My Dog Suddenly Acting Aggressive?

I live with my boyfriend and we have a 1yr old Papillon male. He is extremely friendly with all people and animals he encounters. He has had a few instances where he has shown aggression when trying to take food from him but this hasnt happened since he was a lot younger. In the last month or so he has snarled at my boyfriend twice and tried to bite him. Both of these times have been when the dog is sitting or laying right next to me and my boyfriend is trying to pick him up. It seems to me that he is being possessive of me and is trying to bite so that he is not taken from me, even just to go on a walk. Any other time the dog will run up to my boyfriend and greet him enthusiastically and he clearly cares for him a great deal, but I am concerned by this sudden change in his behavior. Our dog is crate trained and we have a young kitten as well that he treats like a loved brother. Overnight the dog sleeps in his crate and during the day he is left out around the house. He has never had professional training but knows “sit, stay, get down, lay down, get the ball, and drop it”.