cousin's son

Q: I am a woman. I have received a marriage proposal from my maternal cousin for his son. My query comes here as I have never considered him with any other feelings except as a son/nephew as he born to my cousins sister. And now my doubt is as I have felt him as my nephew/son, is it permissible for me to marry him? Will my marriage with him be accepted by Allah? Earlier I have considered him as something else, and now I am entering into Nikah with him.