I agree with
@chickens really. We call it "jealousy," that's our name for the human emotion, but in the animal world it is territorial possessiveness or other resource guarding. For animals it's a necessary survival instinct. Mother animals must be protective of their babies, males must guard their mates and sometimes their territories. Your pet learns that if it whines, dances or exhibits certain other behaviors we will pick it up, give it a treat, cuddle it, or reward it in some other way. We often like it when an animal acts protective or possessive of us. We equate it with love and/or jealousy. It's endearing to us, but it's a survival instinct to the animal. We are the Great Protector. They value that relationship and they don't want to lose it. Sigh. Nobody is going to like that, it's cold and clinical. But animals don't have the same emotions we do in this regard. I'm not saying they don't love us, they do. It's just different.
ETA: Just my opinion, of course.