Oh? What's this? Human-human romance?? And dog jealousy???
It's this. He's protective of his owner (in a turbo-tsundere fashion) and now that he's human he can vocalize that protectiveness. There's nothing romantic behind it, getcher minds out of the gutter, I live therecould be a love triangle? not romantic love from hibari (he doesn't feel much of that to anyone) rather a platonic love? this is his "owner" so he would not anyone anyone near them.
It's this. He's protective of his owner (in a turbo-tsundere fashion) and now that he's human he can vocalize that protectiveness. There's nothing romantic behind it, getcher minds out of the gutter, I live there