If you now have evidence that you have been living with your partner for around three months (or more), that is probably your ONLY choice out of what you have mentioned as you want to stay long-term in New Zealand.
Your brother might offer to sponsor you financially, but there is no way for him to sponsor you
for a visa. (There used to be, but that ended many years ago now.) A visitor's visa is ONLY for people making a temporary stay with a plan to return to life and work in their home country afterwards.
See old threads here
https://www.google.co.uk/search?sour....0.wQvX0lW-8nQ with discussion and examples about evidence of living together.