Why does this baby make me so happy?

My cousin my bff had her son and at first her annoyed me to death but after he lived at my house for awhile I got attached to him and yes I cried when he went back home, I love when he gets cries when I leave? And how he calls my name when I drive up to his house, I live to make him happy? I've had such a change of heart with him and I love that he feels safe with me and cries when I pretend to go bye bye...what's going on...and no I don have my own kids but I even get jelouse when he pushes me away 2 be with his own mom?? What's wrong with me?