I see you're 28 years old. Certainly old enough to make an adult decision about how and with whom you want to live your life.
One thing I'm not clear on, are you living with your parents now? I'm also wondering if they've met your BF, or at least know about your relationship? Do you have brothers and sisters or are you an only child? Also, do you have job prospects lined up in Auckland?
I think it is completely reasonable for you to make this move. I also think, as others have suggested, you consider the possibility that this may not work out. It is one thing to date someone and another to actually live with them. I don't want to sound pessimistic because it may work out just great. But, on the other hand, one doesn't really know until you move in and begin the process of adjusting to one another.
For this reason it is a good idea to have your bases covered in case it doesn't work out. Try not to burn any more bridges than you absolutely have to and try to put in place as many 'safety nets' as you can. You might even consider discussing this with your BF, that you both approach this as a 'trial togetherness' for, say, six months, just to see if it is working for both of you.
Since we don't really know you or your parents it is difficult to answer the 'how to tell them' question. From what you've said it sounds like they may not take it very well. It's unfortunate because if this were a heterosexual relationship they'd probably be thrilled for you.
You probably need to tell them that you love them, respect them, appreciate everything they've done for you but that you've met someone and that the two of you love one another and want to try building a life together. Tell them this doesn't mean they're losing you as a son but that you're moving on with your life. You will still be in touch with them and see them.
Whatever you tell them, you're then going to have to deal with the consequences. They're going to have their feelings about it, whatever they may be. It's difficult but you have to respect their feelings on one hand while not letting them 'get' to you, on the other. Their feelings are theirs and are their responsibility, not yours. I don't know but in your culture that may sound a bit cold but it is a fact none the less. It is difficult for many of us to not feel guilty or responsible for our parents' feelings. Hurting them or upsetting them isn't your intention and there is no real 'need' for them to feel that way. In fact, what they 'ought' to feel is happy for you, happy that you've found someone and happy that you've grown up and are moving out into your own life, even proud of you. Again, if this were a heterosexual relationship, that might be what they *would* feel. So, what's the difference? The difference is in THEM, in their ignorance and attitude about whatever they believe 'gay' is and you can't directly change that. THEY have to change it and if they won't or can't, that really isn't your fault.
Hope this helps and keep us updated with what happens.