He wants me to treat him like my own son

So my cousin who’s only 16 told me once that I treat him like he’s my son and I’m like his mom well last night he told me he wants me to treat him like he is my son and that he wants to have his own room in my house and do everything that I would do for my kids I told him how much I care about him and he couldent believe it he was like really why is he like this he has a mom but he wants me to be his mom