Accepting someone whose gay

Okay so my nephew is about 10 years old and hes been very feminine basically his whole life. Recently though hes been having doubts about his sexuality - even though in my opinion he doesn't really know who he is yet. Hes been watching alot of porn both with female and male' Weather or not he think hes gay i will still love him..  But my sister (his parents) don't accept it. I want him to know that ill be here for him but I don't want to go behind my sisters back even though she knows she wrong I mean hes only 10 I feel like she should just let him live.. Is they're anything I can do to make him feel comfortable?