HELP!!!!!

Hi everyone I really really need some advice I'm in this situation that I am being asked to adopt a nephew I feel really bad because I really do want to adopt him but my partner even all on board with me my heart aches every time I seen this little boy I have three of my own and I couldn't imagine being in my aunts place I have thyroid and most of the time I struggle my partner is more than understanding with me he helps me with the house chores he goes to work everyday I cook for him I clean for him I wash for him I am a stay at home mom he has always been by my side and the good times and the bad times but this time I feel that he's not being supportive but at the same time I feel like I'm asking him for too much I need help I don't know how to tell my mom and my aunt that I can't help them I want to with all my heart and all my being the little boy breaks my heart and I really really do want to adopt him but I feel that if I tell my mom and my aunt that I can't they're going to go against my partner and say that it's all because of him I am from a Hispanic background and to say no to something like this is something that is never forgiven someone please help me what can I do